My comment about over driving if MDM interferes has to do with over driving on the street. Which, let's face it, is what most people do with these cars...street driving "hard".
BMWCCA teaches its instructors to be 100% indifferent as to what traction control a student should use. There's (perceived) liability in suggesting either one. It's totally a driver's choice.
There are two times when traction control are good as far as I'm concerned...when someone is just starting out and doesn't have car control skills and is generally overwhelmed with track driving. The second is when you are more advanced, you turn it on to see if you can drive the track without it interfering. Kind of like an instructor being with you to say dial it back a hair. Drive as fast as possible without it kicking in.
My last point is this. In my head...we all go to the track to become better driver's, learn new skills, and generally just have a good time. As you learn to become a better driver, you should also be learning the ability to jump into any car (or kart or whatever) and drive it fast. You learn to drive fast because of the mechanical abilities of the car...not because the car can save you. How would you ever begin to understand tire pressure, chassis dynamics, or finding grip if you have this third party between you and the road?
The M3 is a challenge of a car to learn on because it's fast and capable. Your mistakes happen at a much higher rate of speed and there's less room for recovery. Having traction control on is great but should really be reserved for the street. IMHO.