I'm not sure there's any concrete evidence to believe that having a male and female parent as a role model is essential or even beneficial. For that matter, even single-parent families aren't necessarily too much of a handicap. The dominant contribution to the child's well-being is stability and love, however that's achieved and whoever that's come from. Just because same-sex families are fairly new, and heterosexual couples were the way it was done for most of history, isn't in itself a reason to favour one over the other.
I don't think it's unreasonable to be a little, shall we say, nervous about the child's prospects with same-sex parents, but that should be a prompt to actually research the impacts, rather than reach a snap conclusion and then stick to it without further thought.