When homosexual relationships have legal sanction, in whatever form, look for the schools to begin teaching the equivalency of homo and heterosexual behavior, including marriage or civil union, or whatever. The problems of legitimizing these relationships will not appear in the current generation, but two or three generations from now, you can expect to see a world in which young boys always begin their sexual experimentation with other boys (as they're simply more available and ready earlier than the girls), and the natural result of that will be more homosexual and bisexual behavior, far less fidelity in marriage, and a debased culture in which to raise children. We've already gone a long ways down that path-- the changes in the world since my childhood in the sixties and seventies are apalling. It will get worse.
If you don't believe that young boys will do this, a while back there was a case in Marble Falls, Texas, a small town north of Austin, where the teacher was delinquent and left the class each day for an hour or so. During that time period, four or five of the boys regularly performed oral sex on one another. How would you feel if one of those boys were your son?
That's exactly how I see it. Our children are not a means to run a social experiment, especially when the results can be so devastating to future generations.