I once watched an episode of Trading spouses on Youtube, where there was a lesbian couple who were raising two kids and a "normal" family raising two kids, who changed places for a week
http://www.youtube.com/watch?v=DtWBeOUTmF8
If anything, it just proves that it's not the gender that matters, it's how the individuals are as people.
If they care for and love children, then I see no reason why they can't raise kids.
The only "issue" are the people who are against it, when it's really none of their damned business.