Do you know why gay people want marriage to be legal for them?

My opinion on the subject? My opinion is that it's a sad day when the only people in our society who see value in marriage and lifelong commitments to somebody you love, are gays and s. Maybe if more people felt the same way, there wouldn't be so many half brothers and half sisters out there with baby mama's and baby daddys. So my feeling is that I don't see how gay marriage is any more "immoral" than the woman in apartment B with 3 kids from 2 different men collecting child support.