The response to similar risks and similar uncertainties varies depending on factors such as whether the risk is consistent with our ethics, whether the risk is freely chosen or imposed, and whether the associated benefit comes directly to us or to society at large or to people other than those bearing the risk. Some substantial risks, such as the risk of injury in a car accident, are accepted willingly because the benefit is large and very direct. A similar risk without such direct benefits may be begrudgingly accepted or rejected. If an estimate of risk has high uncertainty and is inconsistent with our belief system, we may well deny it, declaring the true picture to be lost in the uncertainty. Thus, a decision that seems to be based on empirical evidence to one person may, at the same time, appear to be based on ethics to another because the first person judges the level of uncertainty associated with the scientific evidence to be acceptable, whereas the second person judges it too high.
Uncertainty is a function of the extent and quality of knowledge about a problem.
While society must learn some tolerance for the irreducible uncertainty resulting from complexity, it should be intolerant of uncertainty resulting from a simple failure to collect information or from sloppy scientific technique or interpretation. The costs for collecting this information should be borne by those who will benefit from the action and not by those supporting a precautionary stance. In our own self-interest, even small and uncertain probabilities of risks of large magnitude or irreparable harm must be taken seriously. The best that can be offered is repeatedly finding no evidence of adverse effects. Quality and credibility of scientific evidence can be judged.