Before we can have a rational discussion about who should be Most Valuable Player, we have to dispense with the odd superstition that a pitcher can't win the award because pitchers win the Cy Young Award.
I call this the Golden Globe argument. The Oscars are more important than the Golden Globes (sorry, Hollywood Foreign Press), but no one would ever argue that a movie could not win the Oscar for Best Picture because it won the Golden Globe.
Consider comedies -- a separate category at the Globes, but often overlooked at the Oscars in favor of dramatic movies. (I suppose one could argue that comedies in the Greek sense -- a happy ending -- win plenty, but I digress.) Imagine a comedy that blew away all the other movies. Shouldn't it be able to win Best Picture? Of course if should.
Ergo, pitchers can win the MVP. There are also other arguments: the dominance of pitching in a team's success, the fact that pitchers face more batters than hitters have at-bats or fielders have fielding chances, etc.
The Cy Young is nice, but it doesn't replace the MVP. We have to look at all options.