I have read estimates that perhaps 10% of the human population is gay. And of course, until recently, many gay people were "in the closet," so this presented even fewer opportunities to know a gay person. The only way to reduce or eliminate prejudice is through exposure, as we have learned through the integration of housing, school, and education. The people who seem most prejudiced to me seem to be the people who have had little exposure to gay people, unable to realize they are people, just like anyone else, because they have not had that human interaction that would make them realize this.
The other difficulty I see is the extreme position taken in some religions, that being gay is a sin. It is difficult to persuade people that their religious beliefs might be incorrect, because they are beliefs, having no basis in any evidence that shows that gay people are simply people who want to love as they are born to do.
It is very sad to me to see anyone making judgements on the basis of whom one chooses to love or have sex with. As long as two people are of age, I am not clear on why what they do is anyone's business.