The only thing all extremism has in common is that it's difficult. Whenever an extremism ceases to be difficult it has no problems being adopted. "Capitalism" as leftists mean it would be better redefined as "a political economy defined by the laziest possible productive actions"
IE, people have no special commitment to markets, trade, or the non-aggression principle. Markets, trade, and the non-aggression principle are just easier for a lazy person to do, for the most part.