First, you are not facing 90+ mph pitches. Get a few of those under your elbows and you will not get the first hit. Not even close. Even MLB hitters let them go b/c they know the umpire won't call it. If a computer calls it, more will complain and fewer will be able to hit it. Most get upset now when the umpire calls it in the middle of the plate at the top of the zone.
Second, some of the best pitchers in baseball would never have been there with computers calling the straight zone. There may be 5 waiting to get there but there will be a lot shorter careers. Less time for fans to know players and follow them. There is already this complaint due to free agency. Now, you want to throw in shorter careers on top of that.
Players adjusting to the umpire is as much part of it as adjusting to the pitcher and defense. They have to adjust to the pitch as it comes in. Making the game easier for the hitter does NOT make the game better. The more challenging, the better feeling of reward when something is accomplished. Many competitors and athletes will tell you that.
Also, fans are a little smarter than you seem to give them credit. They may not know the rules of the game but many can stand on their own 2 feet about things. Spoken like a true out of touch computer.
As a computer, you are missing the finer points of the game already in your argument for computers and IR. Very similar to what a computer will do and thus miss the point of having human umpires over computer ones.