The government has a little more than the guns (in the form of the police, the jails), it also has the ability to force resolutions to prisoner's dilemmas and tragedies of the commons that are currently working in
our favor. If corporations ever cut out a group of people that should actually be served (for example, denying loans to capable individuals on grounds that have nothing to do with their financial stability), then there is a Schindler's list motivation for corporations to "defect" and include the group. Then, the market dynamics make everyone else a lot worse off unless they also defect.
America already has one experience with a mechanism that can coordinate non-equilibrium behaviors among companies that would individually benefit from defecting: racism. Government fiat is another such mechanism, and as far as the similarities go, it could produce something of the same results. (Groups cut out of society with nowhere to turn.)