Libertarians and classical economists often use data to support capitalism, so a scientific look at it is warranted.
This isn't a particularly scientific article, though. It's more like "let's cut through all the cynical rhetoric that capitalists use to make it seem like capitalism is good for everyone and not just the wealthy/powerful."
There's tons of examples of the failure of overly centralized, planned economies: USSR, N. Korea, China, Venezuela, Greece. I don't need to test a science report. I just need to have lived for the last 40 years.
That, in spite of the repeated spectacular failures that were caused by communism.
Conflating economic with government / ideological constructs is a common trap. Centralised & planned economies are common everywhere, I think, but in 'the west' they're just masked a bit more creatively -- and, of course, they're not planned by the state.
Now imagine state monopoly on everything, and you're close to understanding what a Soviet-style centralized planning looked like.