The libertarian answer to this would seem to then be "Excellent; now anti-fascist organizations have an optimized channel to get their message to those people."
The market can decide that only one player is sufficient to its needs.
But lately companies like VISA and MC seem to be abusing their semi-monopolies. Try living without a card or bank account.
in these situations, you vote with your wallet by no longer using the service. there are issues with the libertarian "vote with your wallet" theory, but this is not one of them.