One of the memes I read about growing up when I started to develop an interest in political thought is the association of abstraction with the left. The right, by contrast, is supposedly more pragmatic, more concerned with reality and institutions, etc. (I may have read this in Kirk or Nash or something).
Now, I tend to think there's an element of truth here, but we must stress that correlation does not necessarily entail causation. Virtually all of the big technocrats, bureaucrats, social planners, and the like are leftists. The ones who live and work in the real world are virtually all comparatively more right-wing. But zoom out the camera lens a little and I think you'll see this tendency is due more to differences in IQ than social attitudes. The big technocrats are all second-sigma types, with IQs in (at least) the above average range; the doers are all of comparatively modest intellect. Insofar as there's a correlation between social attitudes and IQ, what we're seeing here is probably what, in statistics, is called a mediating relationship (where the relationship between X and Y vanishes once you control for Z, because the effect of X on Y is not direct but is channeled through Z).
I think once you control for differences in intellect, the gap reverses: the rightists become more abstract, the liberals more concrete. Actually, it might be more appropriate to say that at high levels of IQ, rightists supplement their concreteness by acquiring some degree of abstraction, whereas leftists remain relatively flat. The vast majority of even intelligent liberals could not really hope to understand something like Bonald's essay on authority, much less write a coherent leftist equivalent of it, and it's not just because they subscribe to an essentially antiauthority ideology.
In fact, to the extent leftists are "abstract" at all, it is about the nature of concretes. It has to be; what else would they abstract about? Metaphysics, which they deny? Religion, which they deny? Human nature, which they deny? These are people who think you can't know anything you can't experience empirically, for Heaven's sake. They have a clinical aversion to abstraction; they just don't get such things, and assume that anything unintelligible to them must be false or not worth knowing. If you don't believe me, hop on over to Edward Feser's blog and see him periodically grapple with atheists whose opposition to religion is based almost entirely on cliches and embarrassing misapprehensions.
So the ultimate leftist goal is, of course, not something so abstract as the salvation of the human soul, the realization of the good life, or the fulfillment of human nature. It's all political: the establishment of a perfect political system, a perfect law, that runs everything perfectly according to their designs, maximizing their designated virtues, minimizing their denigrated vices. (For more on this, see Dr. Charlton's Thought Prison). It's very telling to me that the main thing for which Jeremy Bentham is known, besides utilitarianism (i.e., about a third of modern leftism), is his proposal for a prison in which a single individual can constantly monitor all inmates without their knowledge.
A logical consequence of this is that most liberals are actually at least semi-decent people who, in good faith, swallow something they don't fully understand (leftists, please don't huff that I'm condescending to compliment you; this is a far more generous concession to my opponents than one could extract from the average leftist sophsticate). It may be true, for instance, that at the highest levels of intellectual liberalism, gay marriage is actually accepted as a means of smashing traditional gender roles, destroying the family, and corroding authority and tradition; but at the level of mundane street liberals, they just think it's a good thing to do. A corollary to this is that while liberalism is inherently opposed to authority, order, and community, the liberal parts of the country tend to be better organized, more communitarian, and just nicer places to live.
When I lived in Maryland (one of the most inarguably liberal states in the country), there absolutely was a sense of community, communal character, and general neighborliness. Crime was largely confined to the ethnic barrios, which were kept carefully cordoned off from the rest of the state. Beautiful and well-maintained parks, safe public playgrounds, abounding history and culture, charming brick sidewalks, and streetlights by the thousands were the norm. Contrast this to the dusty, cultureless "conservative" Texan slum I presently live in, where an insuperable gloom settles over everything in the evening, enabling an army of semiliterate degenerates to emerge and proceed to punch out cops in strip clubs, burn down abandoned buildings, or scream at their women in the middle of a crowded residential street at midnight.
The majority of liberals aren't malicious, though their beliefs are malice given intellectual expression. If they had the capacity to follow their beliefs through to their logical conclusion, most wouldn't be liberals; they'd rather keep the nice communities than let some some homosexual somewhere bugger his boyfriend on the taxpayer dollar. But they don't have that capacity, and the reason is that they are allergic to abstraction.
I've attributed this aspect of the leftist mind to spiritual autism before, a stunting of the soul and a crippling of the mind's transcendental capacities. But whence this autism? I'm still uncertain, and it remains an unsettling question to me, because it is an obvious impediment to grace.
At any rate, none of this really changes anything. There's not much daylight between stupidity and evil. and leftism remains Miltonian Satanism with a sophisticated public relations sheen. That some people buy into it in good faith only makes their ultimate damnation tragic.