No, you should not let him bite someone you do not like!!!! This only reinforces the myth that Pits, especially, are "bad dogs", good only for euthanasia. This also teaches dogs in general that biting is permitted under any circumstances; what happens if you are not around the next time your dog "wants to bite someone," will he know whether or not you want him to bite that person? That will lead to enormous medical bills, and an increase in homeowners insurance, and possibly having to have your dog "put down". Teach him there are other ways of getting rid of those you don't want around.