The focus should not be whether gays/lesbian ability to provide or parent, although it is.
Ask any children you know if they would like to be adopted by gay/lesbian couples. You won't find any.
If you ask teens who are aware of gay and lesbian lifestyle, I received age appropiate answers as to why they wouldn't want to be adopted by them.
The next question I asked, if you had a younger brother or sister, would it be okay for them to be adopted or fostered by a gay/lesbian couple. The answer again was no.
A kid with no parents wants a mom and dad. A kid with one parent, wants and needs a surrogate mom or dad.
An older child wants his/her siblings to have a mom and dad even if she never had any or only one.