First a comment on the Howard's statement "Most human progress does not occur directly from intentional design." I probably wouldn't have written it exactly that way and I don't want to speak for Howard, but I think the point is that there has been a heck of a lot more "intentional design" than human progress and much of the human progress that has resulted from "intentional design" ended up being progress that was completely different than that which was intended. In other words, people have tried lots of stuff, most of it wasn't beneficial, and some that was beneficial had nothing to do with what the people had set out to accomplish.
Ironically, I almost used a Thomas Edison metaphor to help illuminate (no pun intended - alright, so maybe the pun is intended) my incrementalism post. Since Jim has mentioned Edison, I might as well unveil it. Edison tried thousands and thousands of filaments before coming up with a viable light bulb. This experimentation occured after solving numerous other problems (such as getting a sufficient vacuum in the bulb).
All this effort required by a super genius trying to make something as simple as a light bulb.
A human brain is numerous orders of magnitude more complicated than a light bulb and the US has 300 million of these human brains interacting. I estimate that the entity consisting of these 300 million human brains interacting has a complexity at least 20 orders of magnitude greater than that of a light bulb.
Now imagine someone with the IQ of oh, I don't know, say George Bush, or even Bill Clinton, designing and implementing a major policy change, and we have to count on the first design working.
If mankind had been forced to give up candles and gas lamps for Edison's first (or 2nd or 3rd...) attempt, we'd all be sitting in the dark. And that is almost literally what North Korea is experiencing because they attempted to implement Marx's first design without sufficient experimentation. Check out this night time map and scroll over to Asia. You can see the lights in Japan, South Korea, and even Russia, but there are very few in North Korea. North Koreans are sitting in the dark.
Now Jim certainly has a good point when he writes "Nonetheless, for those changes that do get through, the consequences -- both expected and not -- are usually managed within bounds, and if they cannot be managed, the causal activity is discontinued". For sure, Russia has begun to undo the effects of communism after a mere 75 years of misery. Germany recovered from Facism much more quickly, only a couple of decades or so, though the price of recovery included 20M dead Germans (including most of their jewish population). Even the advancement of western civilization was only delayed a thousand years after the barbarians burned Rome. So yes, humanity will no doubt recover from virtually any set of policies our leaders foist upon us. But I'd rather not be foisted upon until sufficient experiments are done.