[MrMon]

If it were simply a matter of aggression, you could breed that out of the chimps. The real problem with domesticating them is they breed too slowly. Take a look at all the animals that are domesticated. Almost all are quick to breeding age, all have young at least every other year. To domesticate, you need a large supply of animals from which to select, as you are literally creating a new species. (Elephants are the exception, but they aren't really domesticated, just trained.)

Once you have a large number of animals from which to select, the animal has to be genetically disposed to domestication, e.g. there has to be something that allows them to become docile. Even if you could get enough animals, sometimes the animal is just going to remain wild. Jared Diamond points out that ideally, Africans should have domesticated the zebra, but genetically, it's missing something found in the horse to allow it to domesticate. No doubt they tried, but ultimately failed, through no fault of their own.

So, great apes simply breed too slowly, plus, they're probably too smart to ever truly domesticate.