The brilliant House of Dumb nails the fundamental flaw of progressive liberalism. (Scroll down to "The Left's New Argument: You're One Too!!!!!")
Liberals disparage traditional morality as irrational and self-evidently absurd, but where's the evidence for their lifestyle ? Civilisation has been around long enough now for us to have a pretty good idea what works and what doesn't. In that sense, traditional morality is just the accumulated wisdom of ages on how to run a society. It's the post-1960s consensus that's arbitrary and unsupported. Are we really living in the one moment of human history where everything that we've ever known about successful cultures no longer applies ?
In a single paragraph, DumbJon has encapsulated everything that is inherently wrong about liberalism - it's premises and perceptions, aims and ambitions, dreams and direction. They are all based on a fundamentally flawed principle that "we" (as in this generation) know better than any other generation that has gone before us.