I suppose, Jason, one of the things that concerns me the most is "letting the genie out of the bottle." Once the system was put in place, there will be calls to use it excessively. Because even though the umpires calls are mostly right, there are going to be charges from the teams for which the call is not in their favor to see if that call should be overturned. If the officials refuse (whether their call was right or, maybe, wrong!) they would be worried about charges that "the fix was in."
From what I take from that mlb.com article I linked to several posts ago...there would, indeed, be a bank of officials glued to TV sets in a NYC bunker--not just one. but they would not be allowed to be proactive. they would only be allowed to react whenever the crew chief on the field deemed necessary.
As Scott noted, the same article said that they would expect those TV umpires to be called into play only ten times over an entire season. I cannot imagine that to be true. First off, if I was running a business and put such an extensive system into operation to be used such a limited time over the course of a year, I would be laughed out of industry. Secondly, I cannot imagine that there would not be undue pressure on umpires to give the electronic eye the chance to "get it right". Why run the risk of NOT checking if the service is available?
Look at the craziness that is Questec. Put an electronic system in place to oversee umpire accuracy and you end up with studies hinting that umpires are racist in the way they call balls & strikes.
Strike zones are amazing things. They are tall and short, skinny and wide. At times, they seem to change from pitch-to-pitch. They are maddening. They are the result of human frailty...and a human's best guess of how to imterpret a standard that was devised by other imperfect humans. Could you imagine MLB proposing to institute ESPN's "K Zone" as a substitute for the human umpire...or even a back-up technology to be utilized if a team feels it was wronged by a particularly egregious call?!? Seems ridiculous, doesn't it? Yet it's not altogether dissimilar from the proposal to use moving video images to determine if umpires HR calls are accurate. Now I clearly see the multitude of differences. But I cite the hypothetical to illustrate how once the silliness is begun, I fear it would be a slippery slope indeed.
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EDIT** I'd rather argue--on any given play--about how the umpires botched the call than find myself arguing about whether to use of replay definitively confirmed the umpire's original call...or, worse yet, whether the use of replay should have or shouldn't have been used in a particular instance.
"We wuz robbed" is a lot better than "we wuz robbed because the TV umpire couldn't see what I clearly saw...which was that the ball was definitely foul!" It's also better than "we wuz robbed because the stupid field umpire wouldn't allow the TV ump to correct the call."