If I kick over the water cooler someone may get wet. If I throw a stick at you with an extremely sharp point it might hit you in the your face, your leg, or your balls. I definitely see a difference and do not consider it harmless.

That ump along with Clemens should have both been ejected from that game. Great example to set for the young ones. Throw things and no one cares, have your tantrum no matter who it may eventually hurt.