the worst one is "it'd slow down the game." it already slows down the game (or stops it, basically) when the umpires huddle up to discuss a call when none of them really knows whether or not the ball went over the fence. then no matter what the call is, the manager who has the call go against his team will come out and argue. if you have replay, you'll have the answer in less than a minute, and there's no reason for a manager to argue the call. i also think that if an ump blows too many calls in a year, he should be fired. they can call this the "bruce froemming rule."