I don't think that you can call this discrimination. From post 1 on I've simply said that sexual behavior should have an R rating. I think you've tried to turn this into an anti-gay thread, when it is actually a pro-child thread. Children should be protected from sexual context, normal heterosexual and gay.
Husband and wife can announce their wedding to a young child as a simple, natural expression of their love toward one another. If wife and wife do it, a question is likely to be raised, and in my opinion should be raised. Otherwise the child could develop an abnormal sense of what is normal. So gay marriage automatically creates a dilemma for a nurturing parent: teach the kid about sex and abnormal sex prematurely, or risk creating a false concept of reality.
With regards to adoption specifically, that means that gay couples should not be allowed to adopt children, unless there is a shortage of qualified, married, heterosexual couples. I don't think that there is any argument against that a married, stable mom and dad is the best option for raising a child.