0. Reality is not socially constructed.
Reality is the set of everything that does not go away when we close our eyes.0 We can disparage this set as much as we like, nowadays, because it no longer includes woolly mammoths that will trample us if we close our eyes too long. Nevertheless, it's still around, the intellectual equivalents of the woolly mammoth are never too far away to be forgotten completely, except among ivory tower tenured academics. Also, in 50 years we might clone Siberian frozen mammoths.
1. Our understanding of reality is socially constructed.
A brief glance at any of the feral children and closet children discovered over the centuries will show exactly why this is so1. We have brains that start out with a few instincts and then pick up valuable information about woolly mammoths, sabretooth tigers, or various other things, depending on the contingencies of our generation. That our understanding of reality is socially constructed is not nearly as profound an insight as some might think.
2. Our understanding of reality is limited.
Our brains did not evolve to understand the universe, to understand humanity, or even to understand themselves.2 They evolved to perpetuate the existence of our pitiful species of bald monkeys. It should come as no surprise that no bald monkey thus far has come up with a self-evident truth that provides a teleological purpose for the universe or our presence in it. It is possible that no such purpose exists.
3. We are bald monkeys. We don't have to make sense.
We are driven by all sorts of desires. Each of the drives we have are justified by the survival needs of our ancient ancestors as applied to different situations. So, our desires conflict.
"Do I contradict myself? Very well then, I contradict myself! I am large. I contain multitudes." --Walt Whitman, Song of Myself
Sometimes we can use some sort of logic to resolve the conflicts behind our desires. Usually we will simply appease the homunculus in our brains that shouts and whines louder than the others. 3
4. We are moral creatures.
Through most of human prehistory we lived in bands of 20 or so, and hunted and gathered. Our instincts are already tuned to a social existence. Even in the state of nature, we lived in groups in which we knew we had to subordinate some of our desires to those of the whole. We knew that there were rules we were expected to obey, and felt at least some desire to obey them. In short, morality is not a bourgeois artifice built to constrain the proletariat, nor is it a conspiracy of the sheep to fool the wolves into denying their nature. It's just a part of us. The moral aspect of our lives shows every time we quarrel. In a quarrel, two people accuse each other of having broken a rule they both have in common. The ability for people to quarrel, even in the most primitive of societies, shows that morality is instinctive.4
5. We are hierarchical creatures.
In the ancient bands of hunter gatherers, one of the males would dominate over the others by shows of fighting prowess. He would be the one to lead hunts and raids, and be the first to rise to defend the group against rival bands. Hierarchies are natural. We accept hierarchies every day, when we obey our parents, doctors, traffic cops, airline pilots, et cetera. It is nonsense to claim that hierarchies are unnatural. It is also nonsense to claim that hierarchies can long outlast their usefulness to their subordinates. Human history is the story of hierarchies overturning hierarchies, and people within hierarchies toppling each other. Some of these hierarchies are what we call our political institutions. These cannot be examined without a look at how they came about in the first place.
"But sir, Delta Tau Chi has a long tradition of existence both to its members and the community at large. -National Lampoon's Animal House
6. Our institutions don't need to make sense.
Look at the British monarchy. Look at the institutions and ceremonies in it. Don't look too long; your eyes will glaze over. Does it make any sense? Of course not. It doesn't need to. The Crown and the Parliament only need to satisfy the needs and wants, material and psychological, of the people of the Isles. The rituals, the ancient laws writ in unknown tongues, and all the rest of the baggage are acceptable despite the lack of theoretical coherence.
And besides, all that historical baggage is what helped the British persevere through the Blitz, and so shouldn't be knocked. For contrast, look at the Soviets, (i.e. the Councils that were meant to rule immediately after the Bolshevik revolution), during the first and second Russian harvest. Here we have institutions founded on an eminently rational theory5, by which they would collect the harvest from the peasants ("from each according to his abilities") and then redistribute it ("to each according to his needs"). Well, it didn't quite work that way.
Peasants were reluctant to surrender all of their harvest, or even most of it, because they did not trust the Soviets to reapportion the harvest fairly. So they hoarded, so the Soviets had little to give the fools who didn't hoard, and those did hoard the next harvest, and so it came to pass that instead of peasants surrendering their harvests to the intuitively obvious virtue of the Soviets, the Soviets came to collect it with the better persuasion of machine guns. We all know how things went from there.
7. Instead of theoretical elegance, an institution needs incremental success.
Regardless of an institution's theoretical underpinnings, it cannot be built in a day. It has to develop over time, and be successful in each incremental goal, just like the British Crown. Since no revolutionary ideologue has the humility, patience, and honesty to go this route, no such person can ever succeed in achieving anything for the benefit of mankind. This includes the late Che Guevara. What is even worse about revolutionary idealogues is their willingness to tear down proven institutions in favor of their pre-alpha hopeless ideas, for what is sometimes called "idealism" but is in reality nothing more than sheer arrogance and intellectual self-indulgence. Keep this in mind when and if you decide to select a cause.
8. Our desires are not the origin of some grand purpose for humanity.
Let's dive back to item 3 and move from there. Our desire to be as well off as our fellows is just that: a desire. It does not mean that communism is the way of the future. Our desire to have our options open is just that: a desire. It does not mean that libertarianism is the way of the future. The alleged "beauty" of an equal distribution of wealth goes right out the window when that equal distribution is an equal distribution of nothing at all, and we're all starving. It is also obscured considerably when we proletarians are well enough off that we find it hard to give a damn how the wealthy are doing. Similarly, the elegant shortness of libertarian doctrine means little to people who have too many other desires and worries to ponder political philosophy. This is especially the case if they just got laid-off amidst a recession. Every political theory is based on a combination of some human desires. None is based on a combination of all of them. None deserves slavish adulation in the guise of idealism.
9. Where a political theory and our monkey naturecome into conflict, theory must yield.
After the first wave of trouble with the peasants, the Bolsheviks had the perfect opportunity to get together and say "maybe this from-each-to-each stuff isn't really workable." But they didn't. Thanks to Marx's dialectic materialist circular logic and assorted descendant mental gymnastics, the old reds had a bevy of excuses to keep on going, and going, and going. In the process they managed to dismiss truth, morality, and a bunch of other human abstractions as bourgeois weapons meant only to stop them. The next bunch of idealogues will do no better. It's one of the nasty things about true believers in any theory about bald monkeys. So, for Pete's sakes, don't be a true believer. In Marxism, Randism, or anything else.
Edmund Burke described a way of thinking of this: don't try to fit people to a theory. Try to fit a theory to people. Of course, if you try to fit a theory to a bunch of bald monkeys, your theory will soon get bloated, heavy, complicated, until it reaches the size of the Talmud. On the other hand, fitting theories to people doesn't kill anyone, unlike the alternative.
Wrapping up: the future.
In the future, there will be bald monkeys screeching at each other and acting out every urge and desire they always have. Communism might go extinct, but democratic socialism will always exist in some countries, parties, and NGOs. So will conservatism and libertarianism. Nobody will ever have a complete victory. What might happen is a victory for the Western liberal model of government, in which screeching takes place in a well structured fashion, while face biting and feces hurling are kept to a minimum. For that we can hope. But if this grizzled rant stops you from becoming a Randroid, an eschatological religionist, or Cthulhu forbid, a Marxist, then I've done some good.
 Not original (obviously). I cannot find the source. Do a web search on "I refute it thus!" and you'll reach similar arguments from Samuel Johnson.
 Victor the wild boy of Aveyron and a several other feral children make for some interesting, if depressing reading.
 E.O. Wilson likes to point this out. Some people like to dunk water on his head. Nevertheless, y'all should read Consilience, by him. Also, Godel's Theorem by loose analogy can be used to claim that a human brain cannot understand a human brain.
Daniel Dennet goes into more depth about this in Consciousness Explained.
 Read the first chapter of C.S. Lewis's Mere Christianity. No, really. Read it.
 Was it hard to read it with a straight face? It was hard to write it with a straight face.