My understand of level sitting is: a character that does not advance in rank for a while.

Why is level sitting regarded with such contempt on the parts of Imms and players?

Secondly, in a question that may be related, why do so many people feel the game only starts at really high levels? It's to the extent that for some extreme holders of this view pk at lower level seems to be held in contempt, like kicking a guy in a delicate place during a boxing match.

And do the Imms share these views?

I'm confused because:
I guess I play a lot of MUDs where reaching the highest levels takes hundreds of hours, and therefore there's no reason to be on the rat race for leveling and instead one has fun and does quests and explores at a lower level. It's no fun exploring an area designed for level 20 when you're level 40! Nor is it fun to level past all the cool challenges and experiences of a lower level character.