Instant replay

The biggest debate these past few weeks among the baseball loving community has been whether or not instant replay is a good idea for the game. I figure it's my turn to chime in.
The first thing people supporting the idea of replay point to is its success in other sports. While it is true that replay has been an important improvement for the NFL, NBA and NHL, the comparison strains under the fact that replay in those sports is practically a necessity. In baseball, there is not the constant activity seen in those other sports. With 12 athletes on the ice, the NHL has four officials skating. The NFL has 7 officials to manage 22 competitors. The NBA uses three referees in order to monitor 10 players. In all three games, that is a lot of action to cover. In baseball, there is one person designated to monitor the one thing going on, be it the pitch, the play at first or the fly ball in the outfield. For the most part, umpires don't need the help like officials in other sports need.
Part of the mystique of baseball is that it is a game designed for intelligent fans. Statistics are so easily interpreted and derived, situational defensive positioning and hitting so prominent in the game. One of the mental facets of the game is getting inside of a hitter, convincing him that a fastball is coming and dropping in a curveball, busting him inside, things like that. Smart pitchers, like Greg Maddux, are in demand because of their command of that fluid entity that is the strike zone. Not only that, but Maddux, through his years in the league, has garnered the respect of the men in blue, and perhaps a little leniency on the corners have allowed his Hall of Fame career to continue, as he doesn't have to throw in a smaller window, allowing hitters to key on pitches that have never been overpowering. As stupid as that reasoning may be, it is and has been a fundamental aspect to the way the game has always been played and shouldn't be altered.
That being said, as the other big three sports have advanced technologically, or in the NFL's case, fundamentally altering the rules over time, replay has been used to keep up with these changes. The NFL has seen itself evolve from a running oriented game to embracing the forward pass, necessitating several officials downfield as the area of action can quickly change by 30-40 yards. It's easier if there are cameras available as back up. In the NBA, a red light flashes behind the backboard when the time runs out, eliminating any equivocation on whether or not a shot was fired off before time expired. The NHL uses replay to determine the validity of questionable goals, as officials often need to navigate their way through 4 guys in their ever more bulky pads and simply can't see what just happened. The game of baseball has remained relatively unchanged for decades.
There is one exception. Every stadium is different, and MLB has managed to deal with that by allowing for specific ground rules from stadium to stadium. Different stadiums also have different iterations of outfield bleachers that umpires must become familiar with from city to city. Because of this, because there is so much going on with a home run call, I have no problem with replay for situations where the veracity of a home run call is questioned. It sounds like that is what is on the table, so hopefully that's where it ends.