Now I will say, in actuality, that I do think I, or others on this board, could be a good general manager, if we had the right connections that you obviously cannot acquire without being in the league for a long time first.
Implementing a team building philosophy and the minutia it entails (contract negotiation, the math involved in salary cap management, managing personalities, etc) are things that lots and lots of lawyers, accountants, managers, executives, etc, are absolutely capable of handling.
Coaching is different. I'm pretty sure I could be a GM though. What I, and many others on this board, lack is the ten year playing career to establish good rapport with other GMs, coaches, agents and players.