I've always assumed this (and assumed that other people assumed this), because if you talk to homophobes they'll eventually say something like "it's a choice!" because it's a choice for them. It's not a choice for me because gay porn doesn't turn me on -- and if it did I wouldn't care anyway because that's how I was raised. But it DOES turns them on, AND they were raised in an environment where this is THE WORST THING EVER, so it upsets them and they get all irrational and punchy (lesson learned: DO NOT discuss this theory with a homophobe.)

TLDR; IMHO Homophobes who think orientation is a choice are closeted gays because logic.

It would be nice to see a better study. Interesting if one hasn't been done in all this time...