Ugh. I may have major issues with the cultural eating disorder that is the US diet, but chainging Cookie Monster ain't gonna fix it.
In fact, if you want to get analytical about it, Cookie Monster is an outlet to the innate instinct in most kids to pig out on cookies. Just like each of the Seasame Street characters gives flesh to some part of a childhood personality that kids associate with, good and bad--grumpy tantrums for Oscar, gluttony for Cookie, overactive imagination for Grover, trusting naivete for Big Bird, etc.
They give the kids something to connect to and see the things they feel acted out, and they illustrate how these things aren't always constructive--Oscar is grumpy, and gets cheered up sometimes, Cookie Monster eats everything in sight and feels bad about it sometimes.
PC-Cookie Monster is no longer a "role model" for kids, consuming a pile of cookies plate and all, then going "Oops" and gently reminding kids that even if you want to, maybe you shouldn't, he's just another parent figure reminding the tyke what to do, and as a result will probably be ignored.
So not only is it stupid, but it's technically stupid, too.