There are some mainstream denominations that have moved away from Bible and have pursued a modern "theology", rejecting Biblical truth for their own modernized "truth", and this was a major reason why these mainstream denominations have declined. There are also "liberal" and "progressive" churches as well. Many of these latter ones are only "Christian" in name only (some of them don't even believe that Jesus Christ literally died on the Cross). And there are outright "gay affirming" churches, filled with homosexuals and lesbians, with LGBT clergy and everything. Even in my small southern city that I came from, there is apparently such a church.
There have been numerous "arguments" for why these churches can accept gays, lesbians, and bisexuals, but do not be fooled: The Bible makes it clear that homosexuality and lesbianism are sins and outside God's order. And not just those either; any sex or sexual immorality outside of committed, heterosexual marriage, is a sin. To wit:
"You shall not lie with a male as with a woman; it is an abomination." (Leviticus 18:22 (ESV))
"If a man lies with a male as with a woman, both of them have committed an abomination; they shall surely be put to death; their blood is upon them." (Leviticus 20:13 (ESV))
"For this reason God gave them up to dishonorable passions. For their women exchanged natural relations for those that are contrary to nature; and the men likewise gave up natural relations with women and were consumed with passion for one another, men committing shameless acts with men and receiving in themselves the due penalty for their error." (Romans 1:26–27 (ESV))
"Or do you not know that the unrighteous will not inherit the kingdom of God? Do not be deceived: neither the sexually immoral, nor idolaters, nor adulterers, nor men who practice homosexuality, nor thieves, nor the greedy, nor drunkards, nor revilers, nor swindlers will inherit the kingdom of God. (1 Corinthians 6:9-10 (ESV))
"Now we know that the law is good, if one uses it lawfully, understanding this, that the law is not laid down for the just but for the lawless and disobedient, for the ungodly and sinners, for the unholy and profane, for those who strike their fathers and mothers, for murderers, the sexually immoral, men who practice homosexuality, enslavers, liars, perjurers, and whatever else is contrary to sound doctrine," (1 Timothy 8-10 (ESV))
We should note here the difference between homosexual acts, and homosexual inclinations and attractions. Its the difference between committing an act and being tempted to do it. The Bible never condemns anyone for being tempted, only for giving into that temptation and acting on it. Struggling with temptation may lead to sin, but the struggle itself is not sinful. The Bible characterizes homosexuality as outright disobedience towards God in Romans, and those who practice it are "given up" by God to do it, three times (in body, mind, and spirit), so that they can do it being given over to "a reprobate mind, to do those things which are not convenient;" (Romans 1:28 ). 1 Cor. 6:9 outright proclaims that those who commit homosexuality transgress against God's order, and will not see the Kingdom of Heaven.
Some people may be born with a greater susceptibility to homosexuality, just as some people may be more susceptible to falling into fits of rage, but the Bible never accepts a person's natural inclinations as an excuse for sin.
The Bible calls all, even homosexuals, to repentance. In fact, after condemning homosexuality, 1 Corinthians 6:11 says "And such were some of you. But you were washed, you were sanctified, you were justified in the name of the Lord Jesus Christ and by the Spirit of our God." Thus, some of the Corinthians were homosexuals, but, through the power of Jesus Christ, they turned away from it and overcame their sin, no longer being defined by that sin.
In the grand scheme of things, homosexual desire and attraction is no different from heterosexual extramarital lust, as far as the Bible is concerned; both are lusting after something God has declared forbidden, and thus has its ultimate roots in sin. For the Bible, there is no question where homosexuality came from; it is sin. Sin warps human perception and perspective so that our thoughts and desires are warped by it. Homosexual attraction does not always result in outright willful sin on a person's part, but it springs from mankind's inherent sinful nature. Homosexuality is just one more sin against God among many. But all men, homosexual or not, are called to resist temptation, which can only be done with the power of Jesus Christ.
Also, to be clear, the Bible does not call out homosexuality as a "greater sin" than any other. All sin is offensive to God. God's forgiveness is as open to homosexuals as it is to adulterers, and God promises victory in sin to all sinners who come to believe.