This kind of action is asymmetric and unbounded: Anon can hurt MasterCard without cost to himself (presumably) and he can theoretically carry it out for as long as he wants. This can only lead to some kind of escalation if MasterCard (and similar entities) want to survive.
Presumably getting caught and jailed/fined is a potential cost? So it's not an action without risk/cost.
Also, is it better to let those populations suffer in "jail" for generations? (If I was Eastern European, I'd be pretty pissed to have been left to rot until 1989.)
If nothing else, the dictators spread their problems (support of terrorists, atom weapon programs etc).
Look at WW II for what will happen when democracies are pressed. At the start of the war, British military argued against bombing private property (German factories). Compare that to a few years later.
(I guess the place where this is closest to happen next, is Israel and the humongous Hezbollah (/Hamas?) arsenals of rockets optimized for attacks against civilians.)
Point is, those juntas are arguably a blight on humanity that needs to be solved, the longer it takes the worse it might be.
Ah well, this is both after the discussion and irrelevant to Wikileaks.
Edit: Made a bit clearer.
I fully support unions and strikers, however I'm not sure how I feel about this kind of action. The similarity ends with differences such as strikers have names, faces, spokespeople, they decide together if they are for or against striking, it isn't one or more people with nothing to do with the company who makes the decision.