The point is, as Mike said, umps do this everyday.
How many times do we hear people (fans, players, coaches, media) calling for a guy's head because he missed a call at first base? Whether it's followed by an out, or eventually leads to a run, guys vent on the field and that's the end of it.
Hell, I'll bet there are at least 10 bad calls every season that eventually determine the outcome of a game. This didn't.
As I said, I would have liked to see Galarraga get the credit he deserved, but the outcry is ridiculous in the sense that we see this (and much worse) throughout the season. The only reason there's an uproar now is because of WHEN it happened.
There are just too many variables and arguments to be made for overturning even more calls if you overturn this one.