Visa and MasterCard probably want government intervention at this point. Regardless of the approach they take now, their phone lines will be clogged up by opposing views voicing their concerns.

By giving in they have promoted this sort of behaviour as effective which means:

• the opposing side know its an effective strategy
• the appeased side know its an effective strategy for future issues.

If the US gov (or the AUS/UK whomever is housing these lunatics gov) decided to make this illegal IE: payment providers cannot prevent legal business based on their own morality or something like that, then visa & MC could hold their hands up and say "sorry dudes take it up with your elected rep" and wash their hands of the situation altogether.