Because many of them are religious Christian fanatics (nut cases) and the Christian churches teach hate towards homosexuals. And it's not only the Christian church that is intolerant of homosexuality. Many other religions are too. There is nothing about the Christian church that teaches tolerance. They're very divisive. Sad. And yet they try to convince everyone that they're nice people, when what they are is, negative, judgmental, prejudice, intolerant, controlling, censoring, etc..
I may not like the Christian churches views, but I'm not the one going door to door like they (Mormons, Jehovah Witnesses, etc. ) do trying to convince them to try homosexuality or think the way I think. I get these people at the front door of my house all the time, so much so, that I installed an iron gate in front of the door.
Also, the first thing that comes to mind when people hear the words "male homosexual" is BUTT SEX, (especially the unprotected type). Since homosexuals can't do it the "normal" way, then they all must be doing the butt sex nasty. Heterosexuals have the normal pair of parts so the only way they do it is the "normal" way. I know it sounds silly, but this is how many straight people think, cause it makes them feel superior. Even though we all know that BUTT SEX is very common in the heterosexual community.
And homosexuals don't perpetuate the human species, so that automatically makes us less than human in their eyes and just barbaric animals. I suppose their IQs don't allow them to count all of the bisexuals or latent homosexuals in society of which there are many, that also fit into the homosexual category.
Lesbians don't offend society, cause they hold the key to the double standard. Since this is a male dominated society and males get turned on by the idea of women doing it together, it nullifies any explanation that lesbians are also gay. They don't have that equipment, so they can't do the BUTT sex nasty. When people think of two women together they just think of them kissing or light dainty sex.
It also doesn't help that for some reason most, but not all women in society, don't like seeing two men making love to each other, since it kind of reminds many of two dirty and hairy sasquatches together which they don't find appealing
When Brokeback Mountain was in the movie theatres and achieved the widespread success that it did, it was also the top folly and parody of late night talk shows and comedians. And I remember watching one review where a critic said, "There is a scene in the pop tent that evoked an ewww reaction in the theatre in which I screened this movie." Hmmm, must have been a really immature crowd, cause the theatre I saw it in, the audience didn't have this reaction at all, however this proves my point about what I was saying earlier regarding the perception and feelings by the majority of the public regarding male-to-male BUTT sex. And of course if you are a gay male you're obviously one who engages in butt sex activity, correct? (sarcasm)