Story Time:
I know the dudes. I had an ex that was a free-lance photographer for Fueled by Ramen. She was really good friends with a band from Chicago called, Showoff. One of the bands they toured with in 2003 was a very young Fall Out Boy. I tagged along with her to a few shows and met the dudes.
Fall out Boy even stayed with us for Thanksgiving. They were all VERY nice... ESPECIALLY Pete. Given my mode of thought and life, at the time, i got along with Andy (the drummer) the best, as i'm vegan/straightedge as well... and i mean, common... homeboy played for Vegan Reich... THAT'S awesome!
I even got an advanced copy of 'From Under the Cork Tree' WAY before it was released.
Personally I've played in every sub-genre of punk and hardcore since the mid-90's, and these days... the poppier side of thigs have given me the most enjoyment. So i say, good for these dudes. They have pretty legit upbringings, and have been musicians forever. They deserve the glory as much as anyone.
Everyone's entitled to their own opinions, though.