They only end up aggressive if bought up to be aggressive. Rottys are the softest things ever if bought up properly. A shitzu could be the most aggressive thing ever if bought up to be....its just a shame that some people think its funny to bring dogs up to be aggressive and harmfull. I have my boxer when i was young and he was the soppiest thing ever, wouldnt hurt a fly. well he killed my rabbit but that wasnt in a nasty way, he was trying to carry her back to her cage bless as they do with their pups, and she died off shock.