What is it? I think you know the answer: in contrast to classical liberals, the modern ones are socialists who hijacked the word because their true name had been discreditied by the Soviet system.
Socialism, in turn, is not a thought, position, or even theory: it is a state of mind. More specifically, it is a statem of mind wherein one rejects reality. This commitment --- to reject reality --- comes first. Since reality is invasive and keeps reappearing now and again, one starts to develop ad hoc reseaoning that explains away the individual instances of reality. Due to this secondary, responsive reasoning, the leftists look like they have a theory of something. The individual words and sentences make sence and mislead one into thinking that one can discuss the matter with the leftists.
Obeserve, however, what happens when you do start to discuss: the opponents do not disagree with you on interpretation --- they deny the facts. In application to the current events in the Middle East, this denieal is twofold. Firstly, the media purposefully ignores what Palestinians say in Arabic, consistently and without variation, and support their words with acts; namely, that their goal is Judenfrei Palestine. Secondly, they also ignore most of what Israelis announce or find, which includes even documents. Arafat signed a check for a suicide bomber --- ignored or explained away by rape of logic. PA has sent a letter inciting the Israeli Arabs to revolt -- again, ignored or explained away.
This has not always been the case, as you know. For a brief period, the Jews were victims and the focus of sympathy. Then women; then; homosexuals; then homeless; then Russians; then Palestinians. Observe how the problems are never solved, they are just substituted by new "causes:" this makes for an easier yet self-righteous life. Does any liberal even talk about the events in South Africa? Of course not, he moved on.
One disagrement I have with your post: Raimondo and the fictitious H.R. Gross --- who, I believe, has never participated in any of the discussions (he/she mostly posts Raimondo's garbage) --- are not even leftists. Raimondo is a self-hating Jew, whose sole purporse in life is to resists the "Jewish occupation" of the world. Thus, you give him too much honor: leftists at least have a respectable goal but start out to acheive it rather badly; Raimondo's goal is neither novel nor moral.
Incidentally, I did not mean to imply that leftists have monopoly on denial of reality: witness, for instance, the conspiracy theorists here on FR and elsewhere. The selective attention to and retention of facts by anti-Semites and other bigots is also noteworthy. Having noticed the same pattern in Raimondo's post, you may have assumed that he is a leftist. I do not think so: he appears to be a regular anti-Semite of Bobby Fisher variety.