Adult subject matter?

For the first time in its history, The Simpsons was preceded tonight with a warning — white type on a black screen — that the show would contain adult subject matter… namely, the subject of gay marriage.

Huh? Is this topic so radioactive that it merits a special warning? The Simpsons has gotten away with a lot of racy references in the past, and gay marriage is talked about all the time on the news. It’s not as if this cartoon was going to show explicit gay sex or anything. Sheesh.