--gays create families whether married or not? They have kids biologically and every other way that straight couples do. In some cases they have to overcome even more obstacles to do so, indicating very strong desire for family.
--including gays in the govt marriage contract extends the same protections to their children as in heterosexual parent families, meaning their children now have MORE protections under the law than if SSM is not legal.
So overall, if concerns are around children, it's hard to say SSM is not better for kids. No one can stop the relationships and families but the law extends protections to their kids.