Unfortunately, a lot of umps have HUGE egos. They can't play the game so they want to be part of the show too. Thus they bounce at opportunities to create a confrontation where there is none, and relish the opportunity to "send a message" when it's not appropriate.
Even if the rules justify some of these actions, there's no need for the umps to be such jerks to the players to stroke their egos.
Honestly, umps have abused their power for so long, that when a player legitimately abuses an ump (like the spitting incident), not many people have sympathy for the ump.