I see that by making the claim that FDR's New Deal merely "prolonged" the depression as opposed to "intensified" or "made deeper" or "caused" the depression, the writer of this article is sticking to the moderate revisionist line, as opposed to the intensified revisionist line. I suppose this qualifies him as a level- headed thinker in right wing circles these days.
Of course what the article omits is that being a libertarian also means that you never have to admit that you're wrong, since there is no perfectly libertarian societies out there, any failure can somehow be twisted to be blamed on government (while any success can be attributed to 'market liberalization').
No, libertarian societies don't exist today, but they did exist once upon a time. Government was created and expanded for a reason (and no, not just to oppress people, though obviously that was the incentive in some cases).