How about the FACT that free market capitalism is the ONLY system which has EVER worked on a long term basis anywhere on this planet!
The economic systems practiced today in both Europe and in the United States are "mixed economies," which rely on taxation of privately owned free market capitalism enterprise to fund government administered social programs.
The variable is percent government ownership and control. Neither approach anything like Soviet or Chinese style communism of the 50s and 60s.
Standards of living are roughly equal for the US, Canada, Denmark, for example.
So the case needs to be proving the US is better off than Denmark or Sweden.
Just making claims without evidence, does not convert a young voter from Sanders to Rubio for instance.
I see little effort going into this argument. It takes work, and it is more entertaining to listen to Glenn Beck and call Jeb Bush a Mexican or worse, or call George W. Bush a homosexual which has been the focus here, of late.
If I was a 20 something and looked at the discussion on this site lately, I wouldn't waste my time.