As GauntletWizard gets into, it helps when individuals asked (by individuals or circumstance) to be bad feel like they'd be doing something wrong and unusual, which people are less likely to do than things they just feel are wrong.
It hurts when people who have already decided to do bad things exploit it.
Because "That's just the way things are done" is the best way to continue horrible practices. Oh, I'm just going to do this little bit of bribery/corruption/racism; it's not really as bad as practice X in the past. Understanding them is the best way to promote bad behaviors. People are naturally afraid of the unfamiliar.
There's a limit; This is the same argument made by moral crusaders who're against sex education, and that ultimately causes harm. But it's the argument ignored by the D.A.R.E. program organizers, and that has a storied history of being shown (sometimes) to increase drug use[1].
