Whether there is a God or not, or whether one's view of God is different from another, I think there are some fundamental principles we should be able to agree on.
We don't let children buy guns, drink alcohol, or drive cars. Making permanent decisions like sex-change operations seems pretty obviously to fall into the realm of inappropriate for young, undeveloped minds. And a gov't dictating that parents must support such decisions or lose their children seems blatantly wrong. I don't need a concept of God to know that.