The first problem with the precautionary principle is its general vagueness.  Stating that society ought to "err on the side of caution" with respect to catastrophic risks is useless because the relevant question is how much society should err on the side of caution.  Certain risks are too improbable to spend time worrying about, and the precautionary principle does not give any indication of what risks we should care about.  More devastating, however, is the fact that the precautionary principle is ultimately contradictory because there can be risks to inaction as well as action.  Banning GMO foods to avert the risk of ecological interference creates the risks of food shortages and environmental damage from increased farming due to decreased agricultural productivity.  The precautionary principle is useless in this situation.  Worse yet, it is prone to rampant abuse, as every party to a regulation could claim to be justified by the precautionary principle.  There is a significant literature on the other problems of the precautionary principle, so I will not dwell on this matter.  But the point is that it is generally deficient.

It is noteworthy that the precautionary principle appears to be very high regard in environmental circles.  This is probably because the spirit of the precautionary principle captures a very intuitively appealing notion: risk aversion.  Most people are risk averse: this is, after all, why insurance exists.  Risk aversion is also not form of cognitive bias.  Even with perfect information, people will usually be somewhat risk-averse.  Given that a democratic government ought to somewhat reflect the interests and desires of its constituents, incorporating society's "average" level of risk aversion into cost-benefit analysis (CBA) seems reasonable.

From this standpoint, one can view a regulation that eliminates one risk as insurance.  From the usual two-state model, a person's willingness to pay for this insurance is simply the difference between his wealth in the better outcome and his wealth at the point at which his utility function equals the expectation value of his utility from the two outcomes.  For a given degree of risk-aversion, willingness to pay is thus some function of the probability P and magnitude L of the possible loss, say W=W(P,L).  In a similar way that standard CBA uses wage premia in risky professions to infer the value of a statistical life, one could use information from how much people pay for insurance to estimate the function W(P,L).   In a standard cost-benefit analysis one could then allow the costs of acceptable regulation to exceed the benefits by N*W(P,L/N) in a population of size N.

Granted, this process would be highly uncertain in the same sense that valuing a statistical life is uncertain: values cluster around $6-7 million, but range from $0.7 million to $15 million.  Calculating the function W would also be extremely difficult because risk-aversion is very different for qualitatively different risks.  Without delving into the complete details, we can say that any quantitative attempt to address risk-aversion in a social setting, however, is better than the vague handwaving of the usual precautionary principle.  Moreover, this approach solves the problem that occurs when action and inaction each carry risks.  Given the probability and monetized magnitude of each, one can calculate society's "willingness to pay" for averting each risk and then add this onto the costs and benefits from the usual CBA.  Given how tenuous many assumptions in CBA are anyway, this proposition is probably not unreasonable.

Manufacturing and disposal are environmentally detrimental in an enormous number of ways, so it is often difficult to compare the effects of one material with the effects of its substitutes.  Given the exigency of global warming, one starting point is to compare the carbon footprint of a kilo of corn-plastic with a kilo of real plastic.  A little work on Google gives very wide range of answers, that seem to cluster around a 40% or so reduction in carbon.  One study says 42%, for instance.  It is not surprising at all that there should be a wide variance in the carbon footprints of bioplastics.  Much of the energy used in the manufacturing is in the form of electricity, whose carbon footprint per kilowatt-hour ranges from nearly zero (e.g. wind, hydro, nuclear) to very large (e.g. coal).  This suggests that producing a fork from scratch out of corn instead of petroleum probably produces a modest amount less CO2.

But there are complications.  Realize that a lot of plastics are actually recycled, producing considerably less carbon.  I had a difficult time determining a figure for the carbon savings from recycling versus new production, but some sources claim that recycling cuts the carbon footprint of a kilo of plastic by about 50%.  This seems believable, though I wouldn't put too much stock in this figure.  For disposable products like plastic cutlery, this puts recycled plastic on par with bioplastic.  Depending on the energy source used in manufacturing, bioplastic is probably preferable due to the fact that it is more easily disposed of by commercial composting.

What about items like plastic bottles that can easily be recycled?  Conventional bioplastics are not recyclable.  Contamination of ordinary plastics with bioplastics ruins the recycling process, potentially causing net recycling rates to decline.  This is particularly problematic because it is often difficult for consumers to distinguish between bioplastic and conventional plastic.  On the other hand, recycling rates for items like plastic bottles are fairly dismal anyway, so the compostability of bioplastics may give it an edge in disposability.

From an economic perspective, bioplastics also present some problems.  To the extent that manufacturers substitute bioplastics for recycled plastics, demand and prices for recycled plastic will decline.  Recycling post-consumer plastic is already difficult/impossible to do profitably as detailed in a fascinating Economist report on waste.  Even a relatively small substitution from recycled plastic to bioplastic could severely undermine the plastic recycling industry, forcing it out of business or to rely even more on public subsidies that would be more efficiently spent on other forms of carbon sequestration.

Finally, it is worth noting that bioplastics and regular plastics have two very different environmental consequences.  One increases farming, which is quite bad for the environment.  But the other increases petroleum production.  It's unclear to me which is worse, but there is one remark worth making.  Recycling plastic does not actually require any petroleum in theory--it only requires energy.  So recycled plastics don't directly contribute to increasing petroleum production (at least up the recycling efficiency).  Bioplastics, on the other hand, always require a farm to grow corn.  From this standpoint, recycled plastic may have a lesser environmental impact as long as renewable energy is used in production, or as long as the amount of fossil fuels does not exceed to the amount used in bioplastic production.

While I am somewhat uncertain of the relative environmental impacts of both types of plastic, it seems that bioplastics are generally superior for items like disposable forks that would never be recycled anyway, while recycled plastic is best used in products that have high probability of being recycled again.  Like ethanol, bioplastics unfortunately will probably be touted by the farm lobby as part of their wildly successful rent-seeking enterprise to fleece the American taxpayer and immiserate third-world farmers.  One should consequently remain skeptical about their environmental benefits, but welcome them in strictly disposable applications.

The benefits of currency are innumerable and pretty obvious.  Without currency, it is extremely difficult to save or invest.  A person can only acquire goods from another person if the first person has something that the second person wants.  Less trivially, a person who uses bartering instead of money has a more difficult time acquiring credit from formal institutions like banks.  The alternative is to resort to informal loan sharks who may physically abuse delinquent customers.  The list of benefits goes on and on.  Currency is unequivocally good, and excessive use of bartering and in-kind payments almost certainly has a depressive effect on the local economy of a neighborhood.

The more interesting question, however, is why in-kind payments and bartering even exist in poor neighborhoods, when they are nearly absent from more prosperous ones.  One might naively surmise that even if people are poor, currency will still be used because the market price for a good will just drop to the point at which people can afford it.  If two people are willing to exchange in-kind services, there is no reason why that same transaction could not be monetized.  Given that few outsiders tend to venture into the ghetto, lower market prices could sustainably exist there (a ride to Midway airport on the 55 bus in Chicago, for example, passes many gas stations that sell gasoline for significantly less than in wealthier areas of the city).

I have four possible explanations for why this phenomenon may exist.  The first is simply an observation that there is a special type of in-kind transaction for which money is simply unnecessary.  In certain situations, the act of person A allowing person B to perform a service for A is itself a form of payment.  The example that comes to mind from Off the Books is the shopkeeper who lets a homeless man sleep in his store at night to guard it.  The homeless many gets a warm place to sleep during the brutal Chicago winter as an immediate consequence of guarding the shop.  It would be pointless to monetize such a transaction because the service that A provides to B is inextricably linked to the service that B provides to A.

Most transactions, however, are not of this nature.  A second explanation, which could apply to any transaction, is that money is not secure in the ghetto due to high rates of robbery.  Given the poor access to financial services like banks, storing wealth is more problematic than elsewhere.  But it is not as if residents of crime-ridden neighborhoods are robbed every day or even every month, so this seems unlikely to be the whole story.

A third and related explanation is that since saving is less feasible and people tend to have a very small amount of money at any given time, in-kind payments are preferable for large transactions.  For example, if I need a new set of tires for my car, I may not have the necessary amount of money on hand, and it may be dangerous for me to save enough for it because I may be housing a crack-addict relative.  But I could give the car repairman a month's worth of lunches from my underground soul-food kitchen as payment.  As a busy man, this might be amenable to him.  This explanation works partially, but it cannot explain why the car repairman would not just accept daily payments in cash of the amount that I would get from selling my soul-food to someone else.

The fourth and final explanation is the most complicated but much more interesting than the others.  Notice that if a good can ever be sold for X dollars in a free market, there must be someone in the community who is able and willing to buy it for X dollars.  So if a good is sold some of the time and bartered some of the time, there must be some people who can afford to pay for it in cash.  Also, we can safely assume that people will tend to prefer cash transactions over in-kind ones.  After all, you can buy anything with currency, while there are a lot of things you can't buy with your cooking skills.  The conclusion is that there must be a large fraction of people who cannot afford the market prices of certain items.

This conclusion might seem stupid because we have assumed that these neighborhoods are poor.  But if everyone were poor and uniformly so, then the market price for goods would either be bid down to an affordable level or the good would not be sold at all.  Income stratification could produce this situation in which goods are sold half the time and bartered the other half.  If the good were a necessity, then everyone will attempt to acquire the good irrespective of whether they have the money for it or not.  If they have the money, then they create the cash price for the good.  If they don't have the money, then they create the barter price for the good. Alternatively, note that since the poor have little to no savings, the percentage variance of their net worth is enormous.  A street "hustler" may only have $20 on hand one day, but if he finds a shopkeeper who will pay him $100 to paint his store, his net worth has increased by 400%.  The result is that a ghetto resident might be willing to pay for goods some of the time (i.e. just after getting paid), but have to barter other times.  So even in a population with homogeneous annual income, if people have highly fluctuating net worths, monetized and in-kind markets for the same good can coexist.

All of these explanations are likely to contribute to the existence of the non-monetized markets described in Off the Books, but it is doubtful that they can explain the entire phenomenon.  Whatever the cause, these informal, non-monetized markets are good examples of the enormous benefit that currency can have for human welfare.