If you think "it is always a guess" maybe it's just that you weren't good at it. Robot technology will just bring a different set of issues for folks to disagree with.
Just like replay. If more than one person looks at a replay there is a damn good chance that there will be more than one interpretation of the outcome.
I mean look at what we have right now. On every pitch we have a box on the screen that is "supposed" to represent the strike zone. Now pull up the rule book and read what is says the strike zone is really supposed to be. Not even close.
Do umpires make mistakes? Sure. Will robots? **** yes. Whether you want to believe that or not. I still umpire slow pitch softball at the park & rec level. Just about the easiest level of umpiring you'll find. Do I get every call right? Nope. But I do the best I can do. Hell, if I walk off the field and both teams are pissed off at me because of one call that went against each of them I figure I had the best day of anyone on the field.
Nobody's perfect. No umpires, not players, not coaches / managers and sure as hell not fans.
If we're going to fix one of those with robots, why not robot players as well?