I like having the human element of umpires/referees in all sports. You won't find a sport without certain judgement calls that can be made by the refs/umps that can dramatically change the outcome of the game, but it's been that way since the inception of those sports and I don't want to see it changed now. I've had my teams lose because of the refs/umps and I've seen my teams win with a little bit of their help. It goes both ways but it's part of the game. Just like foul calls in basketball, and pass interference in football, balls and strikes are a judgement call made by the umpire. Most of the time they'll be right, but they'll get some wrong. The thing is, they'll get some wrong for every team. My biggest issue is umpires who don't have a consistent strike zone for both pitchers. When the ump's strike zone is at least consistent, even from game to game, the pitchers and batters can figure it out and it's no big deal for either team.
All that said, I would like to see them give each team X number of challenges that can be used to challenge the ball/strike call, similar to tennis where they use the computer to challenge whether a ball was in or out. With all the technology and all the cameras on the fields, everything should be challengeable, in all sports. I hate it when I hear the announcers say "that's not challengeable". Well why not? That's just pure silliness.