This is the first time I've heard this question that begs a response from me; "Why after over 2000 years is the argument only now being made for the acceptance of homosexuality in Christianity?
I think this is a legitimate question with a few answers.
The first thing you have to understand is this question is asked on the assumption the "Church" has always gotten it right with the right way of treating others. When you look at history you'll see the church has done the exact opposite of getting it right with it's treatment of "groups." Exploitation of animals, persecuting Jews, Protestants... persecution of Jews again... and again... and again, seeing a women as less of a man, a black man or woman as less than a human. Religious persecution in England is what founded this country. The list goes on and on and all had a justification from the Bible. I see nothing different with what is happening with homosexuals now. Again, Law trumps mercy for one group and gays are somehow outside the gate of "Love your neighbor as yourself." The early church that was persecuted for their faith in Christ would rend their garments in grief and pain knowing the church would turn the tables and be the ones now doing the persecuting, ten fold.
For people calling the acceptance of gays into the church heresy, it just doesn't fit the definition. Every heresy started with either one individual or group at a starting point. What you see with gays becoming Christians and straight Christians accepting them is a great moving of the Holy Spirit, independently, all over the world at the same time. The Presbyterians church just now made the judgment as a church body to accept gays unconditionally while gay-affirming Pentecostal churches in Brazil are exploding with new converts. From Evangelical mega-churches in Texas now embracing gays to gay voices within Orthodox Judaism finally being heard. Something is going on with homosexuals that is bringing them to God in a time like never before and God reaching into so many hearts with telling people; "Accept these who are Mine." The Bible did say God will pour out his Spirit in the last days. I truly believe gays are the last group to be called to join the Kingdom because as a community I believe they were only now mature, ready and willing to accept God's calling to multiply His Kingdom.
I think the final answer on this question is answered by the Bible itself. More and more people are becoming the Bereans Paul wanted them to be. Searching Scripture for what is the real Word of God and not just trusting "church men" and their traditions to take their hand with leading them, hence this blog with me making a sound, Bible-based, case and why I keep adding names to my list of gay affirming scholars.