Richard of the Dystopian Pokéverse asked yesterday for people who support level caps to explain why they are correct without sounding like a crazy racist. I didn't answer in the comments of his post, because although I use level caps, I don't know that I can claim to support them. But I do have an answer.
D&D is biased in favor of humans. This is not "racism"; it's a side effect of the fact that only humans play D&D. We haven't made contact with aliens, we're still struggling to communicate with chimps and dolphins, and no one took up my previous challenge to create a D&D game for dogs. So, humans are the only example we can use as a baseline for playing a fantasy game, and sentient beings which are different enough to be considered "non-human" must be played as freaks. Any class available to humans is thus defined from a human perspective, and any member of that class who is not human must be described in terms of exceptions to the norm. A dwarven fighter is a fighter in the context of human culture, but with certain exceptions.
Now, in my game, I take this further and make dwarves and elves rare (and halflings even rarer.) So, a dwarven fighter is literally a dwarf operating in a human context. Since the fighter class is linked to the human feudal structure, you have to ask "if a non-human fighter reaches 9th level and establishes a barony, how will the human population react to this?" For that matter, since "level" is partially a matter of reputation, would a short dwarven fighter get the same amount of respect as a human fighter?
For this reason, the fighter class is capped to 8th level for any non-human in the game as I run it; dwarves, being 3/4ths human size, are capped to 3/4ths of 8th level (i.e. 6th level.) Halflings, being half human size, are capped to half 8th level. That's as far as either race can get without extraordinary measures. The reason why I say I don't support level caps is because I am open to in-game solutions to get around the level cap; if you want to be a dwarven baron, figure out an in-game way to make the human population see you as worthy of the title.