If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
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As others have pointed out traditional liberalism and "live and let live" long predates post-modernism. On the other hand, the recent surge of "liberalism" really anti-nominalism masquerading as liberalism. Is caused by the "no objective truth" attitude of post modernism.
Do you mean antinomianism?
(If so, I think your characterization of it is obviously wrong; there are plenty of moral principles there, even if you find them extremely bad moral principles.)