I would only assume that the author is also saying the Left has also ditched the Neo-Marxist Frankfurt group as they continue to hurl themselves headlong further and further into Post Modernism.
Since postmodernist ethics are basically nihilistic, I never could understand why “the absence of moral absolutes” means that we have to embrace multiculturalism, “equality,” and social liberalism. If they wanted to be consistent post-modernists, they would admit that there is no great moral imperative to promote multiculturalism or “equality” either.