I recall someone (it may have been on this board) explaining the "evil MM" myth in great detail to another poster. As you say, the MMs place the orders they are given. The poster then went on to explain how he could place multiple orders routed through several MMs to make level 2 look they way he wanted. He even offered to demonstrate it for them.
Now, how much one person could actually be capable of and the legality of it all is unknown to me. It did, however, make a whole lot more sense than many of the conspiracy theories offered about MMs, shorters, etc.
Someone with more knowledge here could probably explain in more detail and more accurately than I can.
