[hobbsmann]

assumptions:

-the button will never fold so the times he doesn't raise we will be getting 23:1
-the times button raises sb never 3-bets and everybody else calls in which case we will effectively be getting 15:1 on our call.
-we will assume that our implied odds of hitting our set and the reverse implied odds of being up against a higher set effectively cancel.

Given these assumptions we need button to call more than or equal to 62.5% to be getting 20:1 on our call.

We will assume button is a solid TAG and thus will be raising a lot of suited connectors and large aces on the button as well as mid to large pairs. I would guess that less than 40% of this range warrents a raise on this flop and thus MM should be ok to call here, but I'll leave it to somebody else to come up a with a percentage of a hand range that will raise this flop.