Unfortunately this is not a theoretical issue only relevant to non-Jews. Having talked with people dealing with child abuse in the frum community - they view this as a troublesome reality. One which is harder to aknowledge because there is infinitely more shame involved than normal abuse. One rav told me of a case where he authorized going to the police - but the community activists drove the family out of the country. BTW people involved in incest don't look or act any different than the rest of us.
Here's an interesting interview from 5mos ago with Marilyn Van Debur, 72-yr-old former Miss America turned incest awareness activist. Said she rec'd 8,000 letters from across the country after she, in 1984, went public with her story. Now if that # reflects just those who took the action of writing in, and no doubt responding in cases similar to hers (father-daughter), imagine the greater scope that that implies for the phenomenon generally!
Part 2 of the interview offers more of a look into her father's pathology.
She's the author of an autobiography _Miss America By Day_, which--if you're not already familiar with it--seems to have resonated with other survivors and helped people in relationships with survivors: See here the Amazon comments (never read it myself, but she's quite articulate in the above interview)-
Found it referenced in the Comments posted to the Morris-Rosenblum-Lesher-Rosenblum back&forth. (The comments section on the last two parts of that actually seems to be where the action is.)