I’m not a scientist, so I’m just guessing here. But looking at popular search terms on porn sites, you’ll find a lot of taboo stuff like (step-)mom, (step-)sis, poop, BDSM, gang bangs etc. But just because people find it interesting in porn, I wouldn’t argue that they necessarily want to act accordingly in real life, bang their relatives etc.

Some time back I also read an article somewhere (sorry no source) that taboos in porn can get somehow addictive in a way that you’re permanently looking for harder taboos.

But as said, I have no clue if that applies here or if there’s scientific evidence for/against this hypothesis.

Maybe they can pull back their head into the shell before opening the floodgates.

I could also imagine that the causality is (partly) the other way around. Demonizing homosexuality makes it a taboo for them and taboos are the base for all kinds of fetishes.