Ok, so i read (a bit) more...
Team sports that have officials fail as analogous situations because in those sports players are attempting to cheat, or get away with things as much as possible. The sports reward it - if you can consistently hold, for example, but you only get called one out of twenty times, that's probably to your team's net overall benefit.
Admittedly, I've never played baseball. But I'm pretty sure cheating (other than PEDs, and even golf has had that problem) is not a huge problem. However, sometimes the umpires get it wrong... and no-one says that spectators should have a role to play in officiating MLB.
Anyway, I agree with you in as much as the problem is so small that it is mostly a non-issue, except in the eventual case where an arm-chair official decides the outcome of a major. Which is fine if the player is blatantly trying to cheat, but not at all fine if you can only see the infraction when shown in super slow on a 50-inch or greater HD tv, in relative comfort and with time to study.