To answer the OP, I think it's a combination of different psychological defense mechanisms with which the self tries to create as much harmony as possible (mental self-preservation if you will). Now, I will concede that there are probably some Christians and others who dislike homosexuals because of some inner convictions held sincerely held by them and not necessarily for other, more complex reasons. That having been said, I should bring to attention that most anti-homosexual individuals dislike gays as a result of, among other factors, projection. Now, psychoanalytic theory established by Sigmund Freud holds that those who dislike gays have formed this tendency to reduce the egodystonia associated with having desires towards the same sex while being taught to oppose homosexulity. The psyche uses projection as a means of preserving the integrity of the self. For this reason Freud firmly believed that the most vehement homophobes (e.g. WBC) are really closeted homo- or bisexuals. Before you say "Psychoanalysis! That is such pseudoscience that even Freud's contemporaries couldn't take it seriously!" However, this is just one more case where Freud has been vindicated by modern scientific research.
In the study "Is homophobia associated with homosexual arousal?"
, the researchers gathered 35 homophobic, heterosexual men and 29 nonhomophobic, heterosexual men (they were divided into different groups using the Index of Homophobia). The men were shown pornographic material that consisted of heterosexual, lesbian and homosexual videos. Their penile circumference was monitored for any changes. "Only the homophobic men showed an increase in penile erection to male homosexual stimuli... Homophobia is apparently associated with homosexual arousal that the homophobic individual is either unaware of or denies." You can read the full abstract at the link (American Psychological Association's PsycNET). And on top of the scientific studies indicating mr. Freud's hypothesis is correct, you can always turn to socially conservative politicians, clergy, heads of anti-gay organizations, anti-gay spokesmen, and the list goes on and on. As a very recent example, a Finnish pastor Markku Koivisto (the leader and founder of Nokia Missio (not related to the cell phone company)) was recently relieved of his occupation when it was discovered that he, according to Timo Aro-Heinilä, had "crossed some sexual boundaries" with numerous men. My parents have been to many of his events and they've always dragged me along, but I always had a bad feeling about him. I particularly remember an instance where, when I was about 6, my parents were listening to one of Koivisto's sermons on the radio. I vividly remember him shouting "But they could not control the lust that BURNED within them!!" He went on and on, constantly yelling something about how horrible the lust in his... I mean their hearts was. I asked "Why is he so angry?" At the time, I couldn't understand it but now, at a more mature age, it seems almost too obvious. He hated what he was born as, but since he lacked the skills to resolve the conflict in his psyche he projected his anger of self to another, external target. But then again, what could he have done? He was born a homo- or a bisexual, and there was no way he could change it. On the other hand, the religion which he (most likely) sincerely believed in did not allow him to be that way. Sure, he could theoretically have lived his whole life in celibacy, but that not being an option for him he did one of the only things he could do. And before you say anything about gay conversion therapy, I'd like to note a couple of things. There have been several things that have been researched and certain conclusions have been drawn. First of all, the method which utilizes classical conditioning doesn't work since it doesn't increase heterosexual desires (i.e. at best it might turn someone into an asexual, but it'll never change someone from being a gay into being a heterosexual). Second, in a study of gay conversion therapies, I think the number that got "cured" was somewhere around 1% or less. Third, from what I've pointed out earlier it should follow that those conducting gay conversion therapy are most likely interested in the same sex themselves (though in this case it might not be a bad thing, since sublimation is a much better response to mental conflicts than is projection).
I believe that I, as a Christian, have answered the OP's question well enough. Now, to answer the most recent poster since his post seems rather content-rich and I disagree with his opinions. As a quick sidenote, although I agree with Cypher on the topic of homosexuality, I must refute one of his arguments since it's a misrepresentation of facts. Christians (myself included) disregard the dietary codes set forth in the Old Testament because in the New Testament Jesus appeared to (I think) Paul and told him "Nothing I've created is impure (referring to Paul's instance on not eating un-kosher foods Jesus presented him with in a vision)." Because of this and other Bible passages, Christians don't have to refrain from eating non-kosher foods like shellfish or pork.
KravMagaSelfDefense wrote:...Even a non-Christian can see that homosexuality is a disgusting, disgusting thing; men loving men how they would a woman, and women loving women how they would a man. It really is twisted if you think about it.
 No. All the major organizations (American Psychological Association, American Psychiatric Association, American Psychoanalytic Association, etc) of the relevant science (psychology) say that homosexuality is not a negative characteristic, nor is it a choice. Also, according to new findings in the field of biology, male homosexuality might actually be a positive thing.
A gene that has an established correlation with homosexuality in males causes increased fertility in female offspring. Increased fertility is certainly a positive thing, no?  In a way I can understand your point of view since I was raised to believe it, but even if I personally considered homosexuality to be twisted and perverse I don't ask that my opinion be made into the law, to quote Bill Maher (oh boy, we're getting really off-topic here).
If I happened to be gay, which I am of course not, but for the sake of argument, if I was, I would seek psychological help and see if I couldn't turn myself around, and suppress that lustful tendency in me that I can't even imagine feeling. And if no psychologist, counselor, or neurobiologist would give me an answer, then I'd personally consider suicide. I'm not kidding. Call me close-minded and judgmental, but homosexual love is a sick, dishonorable thing whose wickedness we really need to open our eyes to.
I'm no psychotherapist, but I can say that I've heard many people (personally and non-personally) say that, and in the end it didn't turn out very well. Personally, I don't think anyone can have an outright hatred of homosexuality without some unconscious processes being a part of it (e.g. the opposite of introjection).
Homosexuality is something that came with the fall of Man, and some people do become homosexual due to influences or tendencies - no I don't think it's genetic to be gay. It's an inevitable element of our world. But what do Christians really hate? The sin, or the sinner? Atheists would have us believe that the Bible's express disapproval of homosexuaLITY reflects into its supposed hatred and judgmental attitude on the homosexuAL. On the contrary, good sir, we are taught to love all men as brothers, and because we love them we teach them that their lifestyle is twisted, and morally wrong.
To rephrase, "I love you, but I hate who (or what) you are." If you outright hate someone for who they are, it's impossible to love them. If we extend this logic ("Love the sinner, hate the sin") further, Christians should love Hitler but hate him for what he was. This is a good rhetorical device, but has little substance.
I ask you, if you are an atheist, this question: Why are you so concerned about equal rights for people denied them? Who told you it was morally wrong to condemn homosexuals? Your parents? Your society? Or was it an inner conscience, a voice for which naturalistic atheism has no explanation? You say we should all be treated equally, but why? What equality do we have if we are nothing more than molecules in motion, dancing blindly to the nucleotide sequences in our DNA code? The concept of the value of human life, and the inherent equality of humans, comes only with the concept that we were created equal. It cannot be reconciled, by no amount of effort, with the concept that we are accidents.
Now, the discussion that started with the search of a motive for the "Christians'" dislike for homosexuals has turned into arguments for the existance of God. "Naturalistic atheism" does have an explanation for this. I won't engage in this discussion, but basically it has to do with the viability of communities, the necessity of societies, and the sustainability of civilized, orderly civilizations. You can find out more at this
Wikipedia aticle. Now, there are certain aspects of the mind (like consciousness) that naturalism doesn't (at least not as of now) have a definitive answer to, but they do certainly have an explanation for the evolution of conscience.