You should keep after this theme, as it is absolutely correct. Some time ago I got a call from an editor asking for a book title that explained liberal political philosophy, and I was stumped. Best I could do was the conservative critiques that describe liberalism’s attributes better than liberalism does itself, such as James Burnham’s Suicide of the West, or Kenneth Minogue’s The Liberal Mind (back in print from Liberty Fund; it holds up very well after 40 years). The point is, it is impossible to find the liberal analogue to Kirk’s The Conservative Mind.
Recall, too, Lionel Trilling’s book, The Liberal Imagination (which set Kirk off to write The Conservative Mind, as Trilling dismissed conservatism as no more than “irritiable mental gestures”), in which Trilling took after liberals for abandoning exactly the kind of outlook your last correspondent laid out, namely, the complexity and variability of social life. Trilling detected early exactly what contemporary liberalism has become: dogmatic, closed-minded, and reactionary. Anyone who understood what Trilling meant (and his book can be considered a conservative book today) would be incapable of nonsense about a “war on poverty,” “root causes,” or a “Great Society.” He thought the sources of liberal thought were to be found in literature, which is fine as far as it goes. (Also as a lit. crit., he suffered from the “When all you have is a hammer. . .” limitation.)
But the sources of liberal thought are in many cases the same sources of modern conservative thought, especially John Locke. Conservatism might well be said to have appropriated and become the champion of the best elements of the Lockean liberal tradition. (Norman Podhoretz argued several years ago that had Trilling lived into the 1980s, he would have become a neocon.) Liberalism abandoned Locke in favor of Rousseau and Kant (you rightly mentioned thinkers like Croly for this transition) and Rousseau and his successors, especially Marx, have come to a dead end. This is where liberals avert their theoretical gaze. To confront the failure of the dead-end tangent of liberal philosophy they have followed in the 20th century and today is to look into the abyss. Hence you have either liberal/postmodern theoreticians who are obscure, unreadable and therefore irrelevant, or you have simplistic rants.