And on top of that, how many of us are actively trading day in and day out? The added value there doesn't benefit the vast majority of society.

EDIT: People with pension funds, 401k's, IRA's, and the like are not trading day in and day out. They typically purchase funds which do the trading on their behalf. Most of these funds are controlled by institutions that aren't subject to be skimmed by the MM's as they are the MM's themselves.