An interesting question

[cyba]

I like your reply, racquel.

Gay porn registered as a threat response as though the viewer's life was actually in danger from witnessing gay sex

That makes sense, especially the last bit. Until recently, gay males were
illegitimized (they may still be) by the dominant hetero-sexual culture whose 'psycho-biology' is powerfully procreative and states, outright, that anything else is 'unnatural'..and..'you'll burn in hell (religion.)'
I can easily imagine some poor student, or other, feeling panic and stress when his brain pleasure centre lights up in the lab and his nob twitches while watching guys (or ladyboys) having it off. It's a public event. He might not feel the same reaction in the privacy of his own or some other person's room.

Edit

One day there will be a world which won't care if you're gay, straight, bi, curious or an elephant!!

Maybe, Howsoon. That's what it will take.