By "real capitalism", do you mean a 100% free market with zero government interference? If so, then it's barely ever existed. But this doesn't matter. We don't need 100% free market capitalism in order to know what effect it will have. We can see how reducing government interference in the economy improves economic outcomes, reduces market distortions, and moderates or eliminates the business cycle. We can see how increasing government interference does the opposite. Capitalism isn't a binary. It's a spectrum. There are numerous historical and modern examples of various degrees of capitalism in countries all over the world. We do, in fact, know what it's supposed to look like.