To make a full case would require something much longer than a facebook comment, but I'll put it in a few essential bullet points, and I treat the Left as a spectrum more or less like it's presented in the wikipedia article (from mainstream liberals to the radical left), and my view is that the further left one goes the more deranged it gets.
1. The hostility to capitalist or free-market values and receptivity to socialist ones. Socialism proper has been a complete failure despite many decades of support among the intelligentsia, although a few far-left nuts still proclaim the moral and economic superiority of socialism and evil of capitalism. OWS is but one example. The more mainstream closer-to-center view of "liberals" and "progressives" wants more redistribution, more big govt, in the name of "social justice" and "fairness" despite very mixed-at-best results. The Great Society programs have done next to nothing to reduce the overall poverty rate in 50 years, while nondefense govt spending in the USA (federal state and local) has increased from about 19 to 28 percent of GDP, fueling deficits and debt. Further, their moral justifications for such policies are dubious; they take it as a given, as a dogma basically, that, for instance, there are human rights to healthcare, food, housing, education. They grant to the state (by its nature a coercive institution) the moral authority to dispose of some people's lives - "the privileged" - for the sake of others (the "less advantaged"). This brings me to point 2.
2. The "liberal" as well as further-left moral compass consists of a lopsided emphasis on "social justice and fairness" to the exclusion of a more well-rounded set of values as seen in conservatives. Social psychologist Jonathan Haidt has gone into this in considerable detail (see https://en.wikipedia.org/wiki/Moral_foundations_theory for an overview). The left-wing worldview is so focused on the political as some way of addressing problems or improving lives that they have lost sight of the more foundational need to do soulcraft. I come at this topic not just as a libertarian but more importantly as a philosophical Aristotelian (which makes me more or less a Randian). Central to Aristotle's conception of the good life is the idea of *virtue*, good habits or practices that normally lead to a flourishing life. I hear a lot more about virtue coming from the Right (although it's usually presented as an illicit package-deal with religion). There is more hostility to religion on the Left than on the Right, and this hostility has involved throwing out the comprehensive-vision-of-life baby with the religious bathwater. The Left is more receptive to moral licentiousness and to overthrowing traditional values. The Left also seems very reticent to discuss the problems that arise from the increase in the rate of single-parent families, not just in minority communities where the rates are higher but also among whites (not as high but rising over time). They'd rather shift focus and attention to "addressing the structural/institutional causes of poverty" - again, showing their one-sided approach to moral and social questions. (This isn't to suggest that the left hasn't had insights about the injustices of the mass-incarceration state, the failed Drug War, and such things to victimize POC at a higher rate. But it's not the whole story.)
3. Cognitive biases and a lack of willingness to engage in serious dialogue with the strongest opposing positions. (In the case of Rand especially, left-wing rebuttals involve sloppy and lazy caricatures, poor reading comprehension, massive point-missing - about, e.g., the theme of 'Atlas Shrugged,' "the role of the mind in man's existence," and other cognitive vices. But it goes for the other strongest representatives of libertarian, conservative and capitalist thought such as Mises, Hayek, Friedman and Nozick.) I've brought up the case of reasonable black conservatives/libertarians like Sowell and Williams whom those on the left have determined don't merit engagement or rebuttal. But the pattern is endemic in the way the left operates. A lot of this has to do with the lopsidedness of the academy - lots of leftists and much fewer rightists. This probably has a lot to do with many of the better minds on the right going into the business world and generating value that way. One major exception in the academy is the economics profession which is centrist or right-leaning, and many indicators show that among social scientists the economists have the highest average IQ. In the humanities it's the philosophers and there is plenty of rigorous debate going on between the left-of-center Rawls-types and the libertarian-types, if you bother to look for said debates. (There is also serious scholarship being done in the academy in the area of Rand studies, but you'd have to be intellectually curious enough to seek it out because the left-wing academic mainstream does not to volunteer any such information.)
The cognitive biases are most obviously on display in the way leftists tend to cite and characterize data in connection with capitalism. I point to one such example in a recent facebook post. (The "Leiter" mentioned therein is Brian Leiter, a leftist who runs "Leiter Reports," the most-accessed philosophy blog.) The lack of willingness to engage in serious dialogue with strong opposing positions is all over the place (not that certain varieties of Rightists aren't really bad in this area as well, but I see more of it on the Left; in any case we need a lot more philosophy in our political discourse), but one particularly egregious, disgusting and saddening instance of such occurred at the University of Pennsylvania, about which I already made a link in this thread: https://www.google.com/search?q=amy+wax+bourgeois+values . (None of the facts about faculty behavior during this episode are in dispute.) The lefty resort to the "Racism!" "White supremacy!" charges has become so excessive and so tiresome in response to decent opposition arguments, that it not only grows tiresome but it also damages the credibility of those doing so. It's rather evident to me that Left and Right today don't even agree on the boundaries of what constitutes racism, but the Left appears content to cry "racism" wherever they think they see it, and assuming that everyone else should just go along. But dialogue about the boundaries of racist speech, conduct, etc.? I'm not seeing it. The intellectuals and philosophers are supposed to be of use here but they seem, on the whole, in on the act at the universities (the Amy Wax episode being a manifestation of such dialogue-impoverishment).
I am more inclined to give credit to "the left" when it comes to genuine achievements in social justice and equality, when it comes to things like LGBT+ rights, where all too many conservatives (but not libertarians) dragged their feet for far too long. But it's also the case that a conservative attorney, Ted Olson (who won the Bush v Gore case), made the arguments for marriage equality in front of SCOTUS. https://www.google.com/search?q=ted+olson+gay+marriage Other than some victories such as this, the Left has pushed a number of bad and damaging things under the guise of "social justice/equality." (What's more, the world is too multi-dimensional to reduce social relations to axes of hierarchy and oppression, which is neo-Marxoid talk of "class struggle" in new garb.) Their good intentions don't suffice for moral credit.