I simply wonder about the motivation of certain people. They are mightily concerned that something might happen and do everything to prevent it... but when these same motives are questioned or applied to different topics, they... well, disappear.
In this case here, we have people that state that Jesus set marriage as man and woman exclusively and without exception. As you have admitted, this is incorrent. Jesus makes a statement about marriage between man and woman and how such a union should be handled.
Now you go on and state that "God´s purpose" is the combination of man and woman. But that ignores every lifestyle that does not aim at such a union. Not only the religiously motivated ones, but every man and woman who choses not to get married at all. This, too, is against "God´s purpose". But no one cares. There is no Christian initiative to make marriage, according to God´s plan, compulsory. Why not?
In another recent thread, I asked about the toleration of non-christian religions. According to God´s plan, humanity was created to worship him. But no one cares to stop other religions in your country from adhering to their faiths. Why not?