Outside of such wild cases as the American frontier and Pol Pot's Cambodia, there has never been a purely capitalist or purely socialist economy. And those cases didn't last long and only survived by drawing on the mixed economies beyond their borders.
The US has never been as purely capitalist as it likes to claim, any more than China is as purely socialist as it pretends. All successful economies are a mix of state provision and private enterprise: the argument is over the best balance, which depends on the circumstances and can't be decided by pure theory or ideology.
Most economists agree that our present troubles come from the US and its client economies tilting way too far on the side of unregulated capitalism, and needing a good dose of state control to right the balance. There have been other times when economies have failed through too much socialism (Wilson's UK is an arguable example), but we are very far from that today.