That's a difficult question because in that particular instance, considering that the thoughts are true is not going to be beneficial because sitting with the idea of being a rapist is going to be emotionally harmful in itself. I haven't met anyone with that particular issue but my guess would be that with the help of a therapist, you would learn how to challenge those sort of thoughts, which are known as cognitive distortions. Thought challenging isn't simply saying 'I'm not a rapist' and it's not simply saying 'I am a rapist, so what?'. It entails asking yourself questions whose answers can help sort of bring you back to reality. Things such as, 'Was I ever situated in a place where I could have raped someone? No.' or maybe the answer was yes. 'If I had any urges, did I follow through? no'. Hopefully the answer is no. 'Have I ever harmed anyone in the past?' Hopefully the answer is no. 'Have I ever wanted to harm anyone before?' In asking these types of questions, you can sort of prove to yourself that it is all the OCD talking and these thoughts are not actually accurate reflections of your intentions or desires. I'm just guessing here because I really think that this is a special case that would need to be worked on in a specific way.