PvP has always been a sport determining one's prowess on most every multiplayer game in existence. As long as there is internet gaming, there will be those that battle. Most of the time, you will respawn afterward, making the death trivial. If you still want to be sentimental, it is a preparation for times to come when mobs become sentient and strategic, therefore taking their revenge on us in the same way we kill each other virtually, so we all have to be prepared unless we lean on the server-makers to make it peaceful mode, admins for /killall, and lower commands like /gamemode to enhance untrained troops rather than train them through PvP practices. We are already dealing with such things. Besides, what if a greifer happens to have a weapon? You don' t want to lose your blocks AND your inventory just because you happen to be his lesser in PvP do you?