How, you ask? Well, ponder this.
Say a person went around life with a severe hatred of the color orange. And not as in "oh this orange shirt does nothing for my complexion" hate, but hate as in a sincere belief that anything bearing this color is pure evil, sinful, and must be eradicated. The belief that orange is the cause for all that is wrong with the world. Even going so far as to brutally attacking/killing people for merely wearing the color orange.
You'd think that person was a prime candidate for the nuthouse, right?
Now go over that scenario again, but replace 'the color orange' with 'homosexuality'.