I hear this asserted often, but have yet to see any concrete proof of it."the redistribution of wealth usually causes a decrease in the activities that produce wealth, leaving generous people with much less to be generous with."
The Soviet Union is sometimes lifted up as "proof," but there's no evidence that it was the communist system that caused the lack of resources. Russia has struggled with a dearth of resources under monarchies, and actually its current "light" socialism is showing much more promise than anything it had pre-revolution.
And it doesn't explain why most of Western Europe is doing so well under socialism.