By arbitrarily accepting or rejecting clients, they essentially determine the existence or lack thereof of these organizations. In the same way that Google has suffered legal action for alleged manipulation of search results (though I must credit them for being very consistent in that regard), MasterCard should also be accountable as not just an actor in a market, but a gatekeeper.

A market that's guarded by a couple of monolithic entities with similar interests is not open, and without credit card transactions a lot of international business is essentially impossible. I believe that's too critical an issue to be left to the whims of corporations.

The situation would be very different if we had dozens of easily available credit card providers who would take our money with no hassles. Whether you consider that a failure of the states or the corporations is no the issue at hand. The problem is one of assigning too much power to aisngle entity.