Correction, a lot of the newer Marth players overrate him because he seems very good, but he has definite problems that keep him from really being a top tier character, mainly in the match-ups and the metagame. Most of the older Marth players are very cynical about him.
That said, character elitism really annoys me too, it always seems like claims made by "low-tier" players inherently have less merit, but that's because of a general perception that they're trying to get more recognition for the character then he/she/it/potato deserves, which causes them to ignore legitimate points.
But I guess the thing that annoys me the most is when people say basically, "I'm better then you so you're obviously wrong about everything".
Eh, I really wish we had a more mature community.