Couple thoughts,

First, with regards to the topic of homosexuality, I do believe that the Bible is very clear on the subject. It is a sin. It is one of many sins that falls into deeds of the flesh [Gal 5:16-26]. I suspect of that list, homosexuality might be the hardest ones to resist. However, that same passage makes it clear that it is one, like the others, that must not be practiced.

Christians should reach out to the gay community. God does love sinners [John 3:16-18] and He want to save all [2 Peter 3:9] but it is equally important to remember what he is saving them from. Salvation is from the wrath of God he will pour out on sin and sinners [Romans 5:8-9]. For those who accept Jesus, he has poured out his wrath upon Jesus in our place (aka propitiation) [Romans 3:21-26].

We cannot water down the message of salvation and accept sin because the culture says it is acceptable. The work of the Holy Spirit is to convict people of their sins [John 16:7-11] and saving faith comes by hearing the truth [Romans 10:16-17]. We must do that with love and kindness [Galatians 6:1-2], even when it is unpopular because we are commanded to [2 Timothy 41:7].

Secondly, I have an opinion regarding same-sex marriage in the USA. I ultimately believe that this fight will be lost for the reasons you mention /u/Lientarp. Divorce and adultery are sins, and our decayed culture finds them acceptable and even advocates them in media.

Thus, I think that the concept of "marriage" will end up purely secular and be nothing more than a legal agreement with tax implications. Wedding ceremonies will still occur as today, but will be meaningless as the actual act of marriage will just be the signing of the legal documents.

However, I don't believe all is lost as eventually I bet that fundamentalist/orthodox churches (and synagogs) will stop performing "marriage ceremonies" as a result of legal challenges and instead they will start performing "Christian Unions" (maybe "Godly Unions"?) which will be limited to church members and Biblical standards.

Note, I am not advocating this as a good thing as I would much prefer to marriage remain defined as the Bible defines it. But regardless of what happens to our culture it does not change anything as we must still be prepared to preach the Good News of Jesus [1 pet 3:13-14].