A not-so-imaginary scenario:
Proposition: Less freedom correlates with lower prosperity.
Laissez-Faire Advocate: "FDR's policies lengthened the Depression."
Progressive: "You can't know that. You weren't there."
(Get that? You didn't personally experience it, therefore you can't be sure.)
Laissez-Faire Advocate: "I was there in the 1960s and 1970s. I know what life was like then."
Progressive: "You can hardly be objective about it then."
(Heads I win; tails you lose. If you're personally affected by anything, you can't separate your reaction from the facts that occasioned it. Warmed-over Kant, anyone?)
Laissez-Faire Advocate: "Look at China during Mao and after."
Progressive: "See. It is possible for coercion to lead to prosperity."
Laissez-Faire Advocate: "Ok. Consider East Germany before reunification with West Germany and afterward."
Progressive: "Germany isn't a pure laissez-faire system and never has been."
Wow. And, yet, Progressives feel (I use the word deliberately) perfectly confident rattling off statistics about the results of FDR's policies, debating the Johnson-Reagan era, pronouncing on the economic systems of foreign countries, etc.
It would be nice to have an honest debate with a Progressive. But since their philosophy can only be supported by distortion, cherry-picking data, false alternatives, or outright lies, I'm not holding my breath.