Such arguments are usually deployed to avoid valid criticisms, not because there are none. Indeed, the Obama White House virtually lives by such claims. All of the experts agreed that their stimulus would work; that Obama's version of healthcare reform was both necessary and popular, that weaning the U.S. from fossil fuels will create "green jobs." The evidence on all of these fronts is mixed or weak and yet the president insists constantly that he doesn't want to hear from people who disagree with him on these issues because all the facts are in.
Such arrogance is dangerous. The literature on the unintended consequences of policies crafted by experts is at least as old as the field of economics. Frederic Bastiat, the great 19th-century economist, noted that all that separated the good economist from the bad is the ability to appreciate the possibility of the unforeseen. Nobel Prize-winning economist Friedrich Hayek demonstrated that healthy economies couldn't be controlled by experts, because the experts will always have a "knowledge problem." They can never know all of the variables and never fully predict how their theories will play out in reality.
Right now Congress is debating a financial reform bill that simply commands that regulators predict when an unforeseen crisis will occur. This is like demanding regulators know when stocks will go up or down. If they knew that, they wouldn't be regulators -- they'd be billionaires.
But forget all that. Let's get back to those evil plastic bags. A new study from the University of Arizona reveals that reusable shopping bags, the enlightened replacement for plastic ones, are breeding grounds for E. Coli and other dangerous bacteria. Roughly 50 percent of the bags inspected were found to contain dangerous, potentially lethal, bacteria.
No, this doesn't mean we should abandon reusable bags, let alone ban them too on next year's Tyranny Day. People can clean the bags and solve the problem. That's a hassle, to be sure. But that's the point. There's always going to be a downside to even the best policies, because the experts don't know as much as they think they do. Sometimes, they don't even know they're not experts at all.