Specifically targeting homosexuals for their lifestyle, which scientifically can be seen as having genetic components as opposed to being merely a choice, declaring that they lack the rights in the public sphere, and further isolating them in such a way to make them a focus of God's imminent wrath is why the perception that "homosexuality is a sin" is hateful.
By extension, the hate found in the confines of Christians (whether they intend or not for it to be perceived as hate) is only a reflection of the hate found within it's holy text and through the divine lips of God himself. So frequently we are pressed up against the messages of love and God's mercy, yet where is the mercy when the body chemically reacts and tells the brain that "I am a homosexual"? This so called mercy is nothing more than abominable chains. How can one rise above sin if one's very existence is sinful, by chemical nature and beyond?
If one want to say "everyone is sinful", then we should not be courting the specifics sins themselves; as if one is any worse than the other. This "everyone is sinful" viewpoint is equally flawed, as it puts all people on the same moral level. Rapists and murders are no different than homosexuals and petty thieves. Perhaps in the eyes of a god, all sins may appear to be equal. However, this equality is never evident in our own societies as we judge "sin" by the extent in which they impact and influence life. We choose to say that the murderer is worse than the homosexual because through our mortal eyes we perceive having life taken from us unwillingly as morally worse than simply being a homosexual. However, even bringing up gays in a simple discussion can often lead to dramatic discourse on why they are morally inferior to other, non-homosexual, individuals. We so often say these things blindly as based on the doctrines provided to us via holy texts (in multiple religious beliefs, no less), churches and their priests, and even as far reaching and presumably non-religious as the mass media.
To further this notion, a consequence of thinking homosexuality is a sin is reflected in the sociopolitical sphere. Religion influences all aspects of social life, so I would think there consists a direct relationship between religion and sociopolitical life. Religious people have their beliefs, and they pour out of the church and into the political spectrum. Regardless of what the Bible says on the topic, it is self-evident that the fact that it is considered a sin (by multiple religions, no less) is why it is causing as much controversy as it does.
One may be compelled to say that "God never states that he hates homosexuals in the Bible." In all honesty, I have never read a verse that explicitly states that God hates homosexuals myself. However, there are verses present where we can see that God (apparently) hates specific individuals and types of individuals. There are many verses that prominently display hatred towards rape victims, slaves, young children who act out of line, and so forth. We may also turn to Leviticus 20:13 (which is typically the root of most religiously driven-homosexual debates) and examine how God deems their actions "abominable" and the result for their actions should be capital punishment:
The NAB translation states: "...If a man lies with a male as with a women, both of them shall be put to death for their abominable deed; they have forfeited their lives."
So, indeed, if God hates sin; and homosexuality is a sin: then God hates homosexuality.
But wait! There's more!
To that critique many religious individuals would reply, "God hates the sin, but loves the sinner." This is also an inaccurate rebuttal, as we see in the verse just posted, that punishment for this abominable sin of homosexuality is death. There is no salvation to be found. The sinner is not supposed to have continued life.
To consider some alternative, frequently used arguments we may also examine arguments which imply that the book of "Leviticus" is irrelevant, as it is from the Old Testament. To that there are seemingly many flaws, including one in which we see people following the Ten Commandments as law. They are also from the Old Testament. Even further, modern Jews still use the Torah as their primary holy book; which includes Leviticus. Beyond this, if these books are irrelevant to modern day and are only to be viewed essentially as a historical analysis of a pre-"era of grace" period for Christianity; then what purpose do they really serve in holding any conversation outside of a historical analysis? Additionally, if history may give any sense of reality to the character of god, even if these laws have changed in the current day, it is undoubtedly that god once thought in such a way as this. The influence of these treacherous laws are undeniable.
If one cannot rise above sin, which I understand is not the inherent goal of Christianity, then the purpose of sin itself is to make human beings, animals, and nature suffer as a result. Christ is said to have been a scapegoat for all of these things, a scapegoat to end the cruelty of his father. We can have redemption, but why can we not escape the constant suffering found within this world? We are offered salvation, but many religious individuals only offer damnation to others in hopes they will convert out of fear alone. This may not be a description of every Christian or religious individual, but in the mainstream (and from numerous individual stories we can find scattered all over the internet) it is evident that Christians seem to offer more in the way of damnation than eternal life to those who are apparently on the same level of sin as they. The only difference is that they have invited some deity, of which they cannot provide proof, physical or metaphysical, philosophical or scientific.
There indeed exist arguments for God's existence. However, they have not yet provided the vital information necessary to make a sound judgement that such a metaphysical deity exists. We have the "prime mover", which on the surface makes sense, but it can also be perceived through materialistic measures. At worst, we can examine Pascal's Wager, which is merely an argument for God's potential existence from fear of damnation.
If everyone is sinful, then they are all bracing for the same damnation; whether it be eternal hell fire or merely separation from God. Granted, the sinful Christians apparently go to Heaven; because their sins are covered (though, Jesus supposedly died for the entire world). So in many respects, all sin is the same because it winds you up in the same location (unless you surrender your life to Christ). Even if one perceives damnation itself as having levels (as in Dante's Inferno), there is still eternal suffering to be found.