It sounds to me from reading press accounts that it would please GLAAD more than I thought, what with Marge greeting her lesbian sister with the lame line that just cause you're lesbian "doesn't make you less of a human bein'." Hollywood just always starts from the gay-left assumption that disapproval of sin equals thinking sinners are sub-human. That claim in itself matches "The Simpsons" -- it's a snarky cartoon of Christianity.
If this dork had bothered to see the program he would have discovered that Marge was very vocally pro gay marriage in the abstract, but was upset when it was her sister about to be married. It was hardly some gay rights soapbox. One also fights the tempation to scream, "It's a snarky cartoon period, idiot!". He helpfully quotes his "boss," Brent Bozell III saying, "At a time when the public mood is overwhelmingly against gay marriage, any show that promotes gay marriage is deliberately bucking the public mood." The episode didn't come close to "promoting" gay marriage and it is no crime to buck the public mood, whatever that means.