Orleander,
At least in foster care you will not be under any illusions concerning your situation and left to make your own mind up concerning the world.
If you were adopted by a gay couple suddenly you find yourself forced into accepting a whole raft of politically and socially inspired ideas and possibly having to physically defend those ideas.
Should a child be burdened with that?
The same could be said for interracial adoption. Is that grounds to disallow it?