nah that's a myth. It is only a bad idea if you allow the dog to grab at your hands as well or if your dog has resource guarding and the game is only a game to you. I play tug with Phoebe, it has not made her aggressive, we played with Max and there was not aggression. Neither of them drop/dropped on command and both were allowed to initiate the game, only rule is that all normal rules still must be followed. That means you can't jump or mouth/bite my hands. It's a game.