Does the Bible say that homosexuality is a sin? A lot of people read it that way, certainly. There are other, more nuanced readings that suggest that the "clobber verses" (Romans 1, 1 Corinthians 6, 1 Timothy 1, Jude 1:7 in the New Testament) are considerably less certain and/or more ambiguous than English translations make them appear. There's a decent case to be made that what the Bible condemns doesn't really have anything to do with our modern conception of homosexuality at all. Social conservatives, however, tend to dismiss those arguments as products of sinful people trying to make the Bible say what we want it to say, rather than what it clearly says. So, for the sake of argument, let's assume that those verses do refer to homosexuality, and the Bible does condemn it.
That's still not a massive condemnation. I mean, yeah, there are some strong words in there (it's hard to see "abomination" as a term of gentle reproof) but even if those verses all mean what socially-conservative Christians say they mean, the Bible overall just doesn't pay much attention to homosexuality. You have to go hunting to find those clobber verses, and they're generally included as part of other discussions rather than topics unto themselves. As something that Thou Shalt Not do, homosexuality doesn't even make God's Top Ten list. Compare that with the topic of, say, usury, or divorce, and you'll find that the Bible addresses those issues much more directly and much more comprehensively.
Yet, as a general thing, I don't see Christians threatening to set themselves on fire if divorced people are given the right to (re-)marry, or calling for civil disobedience if we don't make it illegal for banks to lend money at interest. Even those incredibly predatory payday lending places, which are just about exactly the sort of usury condemned in the Bible, aren't what you'd call a popular topic for Sunday sermons.
And then, of course, there's Romans 13:1-7. I mention this one specifically in relation to the Supreme Court decision:
1 Let everyone be subject to the governing authorities, for there is no authority except that which God has established. The authorities that exist have been established by God. 2 Consequently, whoever rebels against the authority is rebelling against what God has instituted, and those who do so will bring judgment on themselves. 3 For rulers hold no terror for those who do right, but for those who do wrong. Do you want to be free from fear of the one in authority? Then do what is right and you will be commended. 4 For the one in authority is God’s servant for your good. But if you do wrong, be afraid, for rulers do not bear the sword for no reason. They are God’s servants, agents of wrath to bring punishment on the wrongdoer. 5 Therefore, it is necessary to submit to the authorities, not only because of possible punishment but also as a matter of conscience."Now this was the sin of your sister Sodom: She and her daughters were arrogant, overfed and unconcerned; they did not help the poor and needy." Ezekiel 16:49
6 This is also why you pay taxes, for the authorities are God’s servants, who give their full time to governing. 7 Give to everyone what you owe them: If you owe taxes, pay taxes; if revenue, then revenue; if respect, then respect; if honor, then honor.