Maligning heterosexual marriage does little to advance discussion. No marriage is perfect. No parent is perfect. That humans don't always rise to the ideals of marriage and parenthood is insufficient reason to surrender its structure to same-gender unions. There is a difference between tolerance and acceptance.
Tolerance is live and let live.
Acceptance mandates that the straights surrender religious beliefs. While some religions appear ready to jump ship when it comes to scriptures, there are many that condemn homosexuality, not homosexuals. Those same religions condemn cohabitation, regardless of gender. Faithful members will hire homosexuals, work with them in the community and help them as neighbors. Just as they would not permit a male PE teacher in the girl's locker room, they decline gay troop leaders for Scout camping trip.