The two most murderous regimes in history have both been socialist ones. Capitalism has proven itself to be less deadly and more prosperous than both socialism

The two most murderous regimes in history have both been socialist ones. Capitalism has proven itself to be less deadly and more prosperous than both socialism and feudalism (which I assume you must be referring to with your "it made it common...", as if there was some idealistic pre-capitalist society to emulate).