I'm against homosexual marriage and especially against homosexual adoption. I don't think it is good for kids to be told that they don't need a mommy and a daddy, that mommy and mommy are fine and we don't need a daddy. I think it is harmful on a level that will not manifest itself for a long time, but will eventually. Kids do need both a Mommy and a Daddy, that is optimal. It is sad when we don't strive for Optimal because of selfish desires of people in a relationship that is destined to be sterile.
Personally, I suspect exclusive parenthood by biological progenitors might do more harm then good. We're herd animals, and it's best if there's a whole tribe that takes care of our young. That there's a male and female in privileged position is just an artifact of how reproduction used to work, and science has fixed that.