Why won't anyone believe me?!

I would like to think that the characters that Sacha Baron Cohen portray; Borat, Ali G and Bruno, they are all to tease the stereotypes in us.

Like how Borat is this earnest guy who may be weird but we should respect cause it's his culture. And Ali G is this junglist who just can't speak good English, isn't very clever and seems to be almost a criminal. Then there is Bruno, the flamboyant homosexual who seems to have really deep but fey thoughts.

Bascially, they represent the -phobes in us. Xenophobes, ethnophobes and homophobes.
Sacha understands discrimination very profoundly because he is jewish. And to be able to translate that understanding into comic relief is not exactly rocket science. But not something anyone can achieve.