Hate to break it to you but gay people come from heterosexuals just like everyone else.<quoted text>
And how do you suggest a world of just gays and lesbians go about having children? If they are not having sex with the opposite sex, how are the children being created?
Your "world of just gays and lesbians" remark shows just how ridiculous you'll get to defend an indefensible position.
Banning marriage for other groups won't protect heterosexual marriages. But making divorce illegal might work.