In addition to what’s been said, keep in mind that:
a) By sitting down to play MG, the players are, by definition, on-board with the idea of tackling the mission the GM sets before them;
b) Players are the ones who define their goals, beliefs, and instincts, not to mention traits during chargen (or template selection), and these are the prime drivers used by the GM for twists and conflicts and such;
c) The dice determine who gets what when;
d) The player’s turn forces the GM into a reactive role as the players take the reins, something that is fairly unique in RPGs.
So, yeah, the GM gets to push pretty hard during his turn. However, he can’t railroad; he can only complicate. On the Player’s turn, they get to push, and the GM has to take a back seat.