As much as we might not want it to happen, but if you write... Especially if you write something provocative... You will have people making the assumption that you agree with them, or secretly mirror their habits. People inevitably blame the author when they feel something goes too far in a book. Just look at the amount of fan distress and outrage when 'Changes' came out. (This is also why I -don't- let my certain family members read my more intense fiction.)

An author I love wrote a little bit about the subject, and I thought I'd share it here.
This is author Seanan Mcguire who's written "Rosemary & Rue" "A Local Habitation" and "An Artificial Night" among others.
http://seanan-mcguire.livejournal.com/280642.html?view=9457986#t9457986