Because they "take marriage seriously" and don't get "bent out of shape" over infidelity...
From "Hurrah for Gay Marriage" by Erica Jong, posted 5/18/08 at Yahoo News
I've never understood the objection to gay marriage. We humans are pair-bonding creatures and we seem to feel safest when coupled. It's not true for everyone, of course, but most of us eventually want a partner to merge our books and lives with. Marriage provides certain extremely useful perks: a partner to be with you when you are ill, someone to share your poverty or wealth with, someone to share your celebrations and devastations, someone to raise children with. You'd think the right wing would be pleased that gay people share the same needs as other Americans.
In the past, gay people had to adopt their lovers to leave them their goodies. Or they had to go without a next-of-kin to depend on in hospital. All sorts of legal mumbo-jumbo was required because marriage was forbidden. And why? Because a bigoted old Bible seemed to imply that God made Adam and Eve -- not Adam and Steve -- as the anti-gay faction likes to say.
I've often found that gay people are better at marriage than straight people. They don't get all bent out of shape about sex for sex's sake. At least this is true for gay men. And they don't run to bust up a perfectly cozy union because one member of the couple -- or both -- has a fling. Some couples are faithful and some not. And they seem to practice this without the territoriality and hypocrisy of mixed-sex couples. Actually, they should be our role models in marriage. They take it far more seriously than straight people -- perhaps because it was forbidden for so long.
Read the rest of the commentary, which goes on to suggest that those who uphold traditional marriage are unable to think rationally and are motivated by economic greed.
II Timothy 4:3-4: For the time will come when men will not put up with sound doctrine. Instead, to suit their own desires, they will gather around them a great number of teachers to say what their itching ears want to hear. They will turn their ears away from the truth and turn aside to myths (NIV).