Usually, I'm a pretty firm supporter of gay rights (I have nothing against gays). I don't support LGBT marriage in a church or other religious place, but I think two gays should be allowed to get a civil union. As far as adoption, I'm kinda torn.
Pros: More loving families to take in orphans/adoptees. A gay couple could have a child if they desire.
Cons: Nobody is ENTITLED to children (they're not rights.) Part of growing up involves influences from a feminine and masculine viewpoint. By giving a child only one of these, they miss a crucial viewpoint and influence on their life.
I personally believe most people are born bi and society forces us into one viewpoint or the other. Going by that, growing up in a gay household might influence the child's orientation. (no proof though)
First of all, it is the choice of each religious institution whether or not to perform marriage ceremonies for same-sex couples, and no one is saying any religious institution should be forced to perform any ceremonies at all, they are free to do what they wish. That being said, there are many churches, including huge denominations of Christianity like Episcopals, who perform gay marriages, and that is none of your business, if you don't like it then don't associate with that church.
Also, in most cases, civil unions are different than marriage, it is not just a difference in words - it is a matter of the benefits they are entitled to. Gay people deserve the same marriage licenses that straight people get from the state, churches have nothing to do with marriage licenses.
Yes, people do have the right to raise children, unless these rights are relinquished by abuse or neglect of those children, which is not unlike how any crime works, certain rights could be lost in the event that they break the law. But raising children is basically the same kind of right as living where you want to and wearing what you want to, it is an uninfringed upon right in normal cases. You don't see anyone interfering with heterosexual birthing of children, regardless of the background or competency of the heterosexual couple (once again, barring the exception of legal violations).
Single parents should be able to adopt, gay couples should be able to adopt, and anyone who is capable of raising children in a loving and caring environment should have that right. And as for the "straight parents are ideal" argument, let me sum it up with this:
It does not matter what is ideal. Adopted children are not a rare commodity. I would venture most permanent homes are more ideal than foster care, and there is the science to back that up. Even if gay parents couldn't raise children the same way as straight parents, so what? THEY ARE NOT COMPETING WITH HETEROSEXUALS FOR CHILDREN.