This thread prompted me to research this topic of homosexual parents in depth.
The fundamental arguments against homosexual couples raising children is that the children will face additional stresses due to the stigma associated with homosexuality and will not develop as well due to not having a mother and a father. These arguments seem entirely speculative.
The first argument does not seem to account for the type of homosexual population that would adopt children. In other words, arguing stresses faced by the homosexual population as a whole would be experienced the same as the population of homosexual couples who wish to adopt children, is statistically fallacious reasoning.
There is compelling evidence that children need exposure to both sexes to have a healthy development, but I could not find evidence which indicated that the parents have to be opposite sexes. It would seem that children can find role models of different sexes outside of their families.
I did find a consistent consensus among peer reviewed research that children of gays and lesbians demonstrated no better or worse development than children of heterosexuals, so the speculative arguments may be moot.
http://www.ru.edu/faculty/rboughner/courses/Alternative activities/Children of gays.pdf