What, exactly, does God have against homosexuality?

Absolutely nothing.

Same thing he has against inter-species sex. It's filthy and unnatural. The sexual satisfaction can only be realized through filthy means which even animals would reject. Religion calls us to be human beings. Every other ideaology calls us to be animals or less than animals. -Granted some sick people have now tried to prove that there is homosexuality among monkeys, which is laughable because in the Qu'ranic narrative the monkey is the lowest metaphor for the human. God created them simply to remind us of the lowness of ourselves and teach us why God is far above his creation [i.e. the Muslim position is that apes are around simply to prove to Christians and other creation-worshippers that God is not a man, or any other creature]. -So, yeah, keep using a freakin monkey as your example in life, see how far that gets you in the world.

Our Prophet Muhammad even said, the closer we get to the day of judgment, we will see people who wake up in the mornings and they are monkeys and pigs... interpreted by hadith exegetes to mean, a person who would have been a decent human being is drawn into an increasingly filthy and crude culture, until one day they find themselves completely corrupted...

Let us not forget that the World Health Organization just 20 years ago listed homosexuality as a mental disorder. -There are psychiatrists and therapists in the Muslim world who actually treat homosexuality as a mental disorder and cure it, and they learned this from Western schools that had this in their psychology curriculum just 40 years ago...

It's an extremely new idea that homosexuality is ok. It has never been accepted by any civilized peoples before modern times except perhaps Rome, and around the time they started to accept that sort of behaviour is when they were ruined and now... not a whisper from them...

It's a deliberate perversion of his design on the part of man (or woman) and a willful break of the marriage covenant instituted by God at creation, a covenant that is reinforced by Jesus in Matthew 19. A homosexual union is a fruitless union.

What does God have against beastiality? If we can eat animals, and use animals for our own purposes, why can't we have sex with them? Because it's a perversion of his design to do, it is a fruitless union.

In the Catholic Church, an impotent person with no chance of being able to reproduce cannot enter into the marriage covenant (if the condition is known beforehand). They are called to live a life of celibacy due to their condition of not being able to produce fruit (children).

While it is true that there are many sins other than homosexuality and all sin is wicked before God, and while it is true that any sin can be forgiven through the blood of Jesus Christ, the Bible does not say that all sin is the same in its effect in this world. God did not pour out fire and brimstone upon Sodom because of its jealousy or covetousness or lack of hospitality. It was judged specifically because of its homosexuality (Jude 7). Though all moral sins are evil in God's eye, homosexuality is especially corrupt because it is a sin against nature itself. It destroys the very fabric of society, which is the family as defined biblically--a man and a woman united in holy matrimony rearing children to fear God and to be productive citizens. Homosexuality is to "change the natural use into that which is against nature" (Ro. 1:26).

In large populations of mammals, homosexual tendencies do arise. However so do cannibalism and murder... The morals are other than natural and to allude to a natural means to justify them is false in the premise!

***EDIT***

This is off the aap (American association of pediatrics)website

Homosexuality is a 'treatable' gender-role disorder

JOHN LESLIE M.D., Ph.D.

Douglas Hamill, O.F.M., M.D., FAAP, has presented a concise argument in favor of the normality of homosexuality (February 1995 AAP News). However, there is an opposing view.

Sociological, psychosocial, scientific and religious reasons exist to view homosexuality as a treatable disorder. To consider homosexuality an abnormal condition should not to be correlated with bigotry or homophobia, any more than considering alcoholism as abnormal would be tantamount to being "alcoholophobic."

APA (American psychological association)

What causes a person to have a particular sexual orientation?

There is no consensus among scientists about the exact reasons that an individual develops a heterosexual, bisexual, gay, or lesbian orientation. Although much research has examined the possible genetic, hormonal, developmental, social, and cultural influences on sexual orientation, no findings have emerged that permit scientists to conclude that sexual orientation is determined by any particular factor or factors. Many think that nature and nurture both play complex roles; most people experience little or no sense of choice about their sexual orientation.

This is a touchy subject. If oyu wanna get technical, absolutely nothing. The fundamentalists are the ones saying about how homosexuality is evil. They give christianity such a bad reputation. The reality of the matter is as long as you don't have gay sex, you aren't sinning as they would say.

absolutely nothing.

before the translation changes the passages, it was man to man and was talking about heterosexual men doing things as pagan rights.

But most would like the bible to say something to support their own personal views.

Reproduction purposes is one. I have yet to find it as on of the ten commandments, so It is not a sin in my perspective, but God has something against not being faithful to one person in your life. To have multiple sex partners at varying times in your life is a sin. It is being lustful.

I imagine it's because of the idea of the sanctity of marriage, but it's most likely because the people who wrote the Bible thousands of years ago found homosexuality to be strange, so they claimed that God hated it.

God created Adam and Eve, He didn't create 2 Adams and 2 Eves, it's just not natural.