Listen, the best reason I can come up with against a KOTOR MMO is the fact that once it comes out, it won't really meet everyone's expectations.
Look at TSL. Supposed to be awesome right? And we still got some diehard fans who do think TSL is awesome, like me. But that doesn't mean that many people who really wanted a TSL was severly disappointed by it...when it actually did come out
. Influence looked good on paper, and everyone was ranting on how great the system would be and how great training other people would be...until it was actually put into pratice. That's the thing. Ideas sound awesome, but once you make them concerte, you get to see its faults.
Basically, KOTOR MMO is going to make people angry. No matter what. Not only will you get these diehard people who hate KOTOR MMO no matter what, but you'll get the people who actually WILL like the concept of KOTOR MMO, but will hate it when they actually enter into the world, either because Bioware happens to be moronic when making said MMO, or because of basic design flaws that is inherent in any MMO game.
Be careful of what you wish for.