My perception is that it comes back to religion. Like it or not, we live in a society which very much accpts very fucked-up Christain values. The term "adultery" is mis-applied to all sex outside of wedlock. Many people seem to accept that all non-procrative sex, even inside wedlock is wrong on some level. Likewise fantacising about sex. Hence, pornography. So if one breaks the taboo about sex, one can still feel guilty if one does not cleanly expunge the underlying wretched meme of Christian morality. There are similar taboos about murder & violence. So if one dabbles in breaking one set of taboos, the other sets of taboos are called into question as well.

I feel that if it were not for Christianity (or religions like Christianity) it would be far more difficult to get people to go and murder/torture strangers who did nothing to them.