A nice analogy by Geoff Nunberg on Language Log:

...dirty words are magic spells that conjure up their references. We first learn about dirty words at an age when we still believe literally in magic, and I don't think anything we learn afterwards palliates their irrational power. That's why we behave as if we could render them inefficacious by the simple expedient of using asterisks in place of some of their letters — magical spells have no power unless you say them just so . And it's why they bleed through quotation marks and the other devices we use to hold content at arm's length: if the New York Times can't allow itself to print "Adam Clymer is an asshole" then it can't print "Bush called Adam Clymer an asshole," either (strong racial epithets have these properties, as well).