Such "laws" or rules of thumb should always be interpreted in light of reason. There's nothing reasonable about paralyzing yourself by entertaining random risks

Such "laws" or rules of thumb should always be interpreted in light of reason. There's nothing reasonable about paralyzing yourself by entertaining random risks or possibilities for which there is no justification. That's as silly as the idea that science is about doubt as a matter of method. It isn't. You don't go around arbitrarily doubting things for no reason because you have somehow convinced yourself that such willful doubting produces knowledge. It doesn't. It produces an incurable skepticism that destroys science. Doubt is the effect of having learned something credible that conflicts with a prior belief. That doubt might prompt us to verify these conflicting bits of information in order to establish some kind of certainty. Chesterton's Fence is a criticism of reformers, revolutionaries, and burn-it-all-down types who want to make changes without making an effort to understand why the thing they want to tear down is there in the first place, what purpose it is serving, and the consequences of doing so. Responsible jurisprudence does this all the time. When judges are presented with a case that puts a law into question, they look at the origins of the law and make an effort to determine the costs of eliminating that law because the good of a lot of people may rely on that law being in place. This doesn't mean they don't change the law if some people would suffer as a result. It just means they are aware of why the law exists and what purpose it serves as well as the relative costs and benefits of doing so (principle of double effect). Naturally, as you have said, we do not have perfect knowledge, so obviously we can merely do the best we can. A person is not obligated to do the impossible.