It's projection. They might not even realize that their struggle with their sexuality isn't universal and that people who identify as fast are the ones that give in to their desires, that denying having those desires is a lie everyone tells to show how strongly they reject that side of them.

It never really clicked for me like this until just now. They don't realize they are different from straight conservatives in that regard, just like it might never have occurred to straight people that two people of the same sex might enjoy a sexual relationship if gays never brought it up in the first place.

If you're conflicted about your sexuality, you're probably not straight (though with lgbt orientations being more accepted and in some social circles celebrated, it might be the opposite if you're feeling social pressure to not be straight). What turns you on doesn't lie.