There's simply too much at stake to leave the possibility of the wrong call being made in major league sports. The most important item is for the correct call to be made. As a result, MLB should implement instant replay as soon as possible. It needs to be done in an efficient way, as to not significantly prolong the games, but it is critical that bad calls are overturned.
By implementing instant replay it would give the umpires a chance to review their call and make the correct decision. I do not believe that instant replay should be used while calling strikes and balls but definitely on plays in the field. Plus most other major organized sports already use instant replay as a way to make the game fair.