There are all these Christian fundamentalists who have been told all their lives they'll go to hell if they're not one hundred percent completely straight all the time, and God sees them and knows what they're thinking. Assuming there's a biological element to homosexuality, a large portion of these people are not completely straight from nature's side. Assuming people are often excited by taboos, they might secretly be more bi-curious (or whatever the word is) than the average population.

For these people, every single step towards gay and trans rights is making it a little bit harder to live in complete denial. They cannot simply ignore it, because they're obsessed with it. One improper thought and they'll burn in hell.

Of course this crowd is terrified of trans people.