(It's worth noting that the "moral wrongdoing is like infectious disease" metaphor is a surprisingly deep aspect of human social psychology, even to the extent that hand-washing affects levels of risk aversion. The pervasiveness of the metaphor is especially clear in the Christians' emphasis on baptism, holy water, purgatorial fires, et cetera. I take about five baths a day, and I suspect it has at least a little to do with constantly feeling guilty. Understanding the basis of this connection might helps us manipulate it: "quietly going along with something even if you don't actually agree with it is dirty".)