I don't like replay in sports, especially not baseball. I enjoy the human element of umps getting calls wrong and teams having to overcome. My only concern with balls and strikes is that they are consistent, in fact I enjoy it more when an ump has a goofy zone for the night as long as he is calling it the same for both teams and then watching which pitchers are able to adjust to his zone. I will miss that if they take it away.
Personally I would much rather assign the top 15 (or however many umpiring crews there are) umpires for calling balls and strikes to be the home plate umpires, with the next 15 being assigned as backups - so each crew has a home plate ump and a backup home plate ump over robo strike calling. That should lower the amount of bad calls but still leave room for the human element over