The show said in a statement,
In light of the feedback we've received on the Katy Perry music video which was released on YouTube only, we have decided we will not air the segment on the television broadcast of Sesame Street, which is aimed at preschoolers.
The statement didn't give any examples of negative feedback, but CBS quoted a couple of YouTube comments: "Thank you for speeding up the puberty process," and "You can practically see her ***." Okay, you can sort of see Perry's *** in the clip (I guess they mean tit? You can kind of see both of them). But it's nothing a kid won't see at the pool or a beach. And seeing images of boobs will not actually make puberty come any faster (although that sure sounds like the kind of lie some older kid would've told me on the school bus).
Time's Belinda Luscombe takes a more measured tack:
Does showing young girls Katy Perry's cleavage make them think that showing cleavage is a good thing? Does it make them more likely to seek out sexual experiences before they're psychologically ready to have them? Does it make boys think Pamela Anderson would be a great president one day? Some studies suggest that children who watch a lot of TV with sexual themes have sex earlier than those who don't.
The first question is the most legit, but Perry's not even in a remotely sexual situation in the video. No one is saying she's hot. Moreover, her outfit is not presented as something anyone should wear to school or work — she's explicitly playing dress-up! And while it's undesirable to suggest to little girls that playing dress-up should be about boobs, that suggestion is being made way more strongly by Hollywood and the Halloween-industrial complex than by Perry's fairly innocent video.
Rather than saying that kids should never see cleavage ever (you'd pretty much have to blind them), we should be helping them dress in a way that feels good to them. One way to do this is to expose them to a variety of clothing styles — which, as Petri of the Washington Post points out, Sesame Street already does. And, as a wise YouTube commenter notes (I never thought I'd utter that phrase):
All this over a little cleavage? And yet Elmo runs around the whole time NAKED!
Is Katy Perry A Sesame Streetwalker, Or Do Viewers Just Want Her To Be? [Time]
Katy Perry: Too Revealing For Sesame Street? [Time]
Katy Perry Too Hot for "Sesame Street"? [CBS]
Katy Perry's Elmo Duet On Sesame Street — A Revealing Moment [Washington Post]