Many abusers are auto-erotic. They are the preferred objects of their own sexual attentions. Molesting or having intercourse with one's children is as close as one gets to having sex with oneself.

Abusers often perceive sex in terms of annexation. The molested child is "assimilated" and becomes an extension of the offender, a fully controlled and manipulated object. Sex, to the abuser, is the ultimate act of depersonalization and objectification of the other. He actually masturbates with other people's bodies, his children's included. - Sam Vaknin