it is actually a (unvoluntary) design choice. when it gets crowded on the screen you couldnt avoid getting hit by some creeps and then you just die without really avoiding it or realizing. if you play to passive you are not able to get a large crowd of enemys with one swing (which was the most fun i think). So i just made the player invincible. You can solve the problem of course by adding another melee attack or a lot of other stuff, but well, theres no time for that :D