see overpopulation is an answer I thought of, of then I thought cats are just as, if not more overpopulated then dogs, but noone cares about mixes etc.. Rabbits are over poplulated as well. I know differnt breeds are for differnt jobs with dogs, but before appearence came into the picture, breeds were mixed all the time in order to better the working ability.

hmm perhaps I should try to rephrase the question. I am not asking why breeding mixes is considered bad, I am asking why dogs are considered differnt from every other animal