As an umpire, I do NOT subscribe to the “human element is part of the game” rationale for accepting bad calls.
I want to get the calls right, and I welcome tools that improve accuracy—as long as they don’t disrupt the game or put the calls under the jurisdiction of someone other than the on-field umpires.
The way this demonstration was conducted makes sense. The plate umpire had the information but he knew the tool’s limitations, such as not being able to measure the 3-dimensionality of the zone, and was able to override when it seemed right.
I would also welcome video replay, especially on plays we know that the two-man system puts umpires in sub-optimal positions.
I’m almost with FenwaySouth: Bring it on—carefully.