A Google Talk by neuroscientist Ogi Ogas, the co-author of the controversial "A Billion Wicked Thoughts". He does not consider desensitization leading to escalation as a possible factor in the popularity of shemale porn. As you will see, he admits to omitting vaginas from their data (you will understand why that's significant). Shouldn't trigger.
Once upon a time, men could trust their penises to tell them everything they needed to know about their sexual orientation.