I enthusiastically endorse Roger Kimball's analysis:
This is the oldest and the best argument for conservatism: the argument from the fact that our actions almost always have unforeseen and unwelcome consequences. It is an argument from so great and so mournful a fund of experience, that nothing can rationally outweigh it. . . .
Progressives cannot wrap their minds (or, more to the point, their hearts) around this irony: that “reform” so regularly exacerbates either the evil it was meant to cure or another evil it had hardly glimpsed.