Is there an arbitrary system of values that will justify capitalism? Sure. There's an arbitrary system of values that will justify anything. Matt Bruenig is therefore fighting an uphill battle:
There is no general framework of morality or justice that supports laissez-faire capitalism. This is a problem of course for those who wish to argue on behalf of it. When you talk to such people, a familiar argumentative pattern emerges that I have come to call Capitalism Whack-A-Mole.
Them: Capitalism is right because people should get what they earn through their hard work.
Me: But...one-third of the national income goes to capital owners who have done no work at all for that income. If you really believe the economic system should distribute according to hard work, then you’ve got to at least tax capital income at 100%...
Them: Capital owners may not produce anything to get that one-third of national income, but they got it through voluntary transactions. I am just against force and for voluntarism.
Me: Transactions are not voluntary. They are coerced through systems of property ownership. You only trade with someone because there is a gun at your head to keep you from simply grabbing the thing that you trade for. There is nothing voluntary about that...
Them: Capitalist institutions may require violent coercion to enforce, but they make everyone very rich. We’d be much poorer, even at the bottom of society, if we got rid of them.
Me: OK. So you support using violent coercion in order to make sure people are well off. But people, especially the poor that you are now concerned with, are better off in Social Democratic systems than they are in laissez-faire capitalism. The diminishing marginal utility of money, by itself, justifies significant tax and transfer schemes under a “making everyone as well off as possible” analysis.If I were trying to justify capitalism with an arbitrary ("deontological") system of values, I would not stop with the three simple examples Matt gives here. I would just move the goalposts. For example:
1. "Capitalism should reward either hard work or risk-taking. Thus, both labor and capital income are justified."
2. "I support conditional voluntarism, not absolute voluntarism. The government should use violence only to protect property rights, and for nothing else. Property rights are defined as blah blah blah..."
3. "I am a pure Benthamite, I care about the sum of utilities; I do not care about the poor more than the rich."
...and so on. In fact, I've heard people say all of these things in defense of capitalism. Matt might manage to smack these down as well by finding some way in which capitalism does not exactly conform to each. But the defenders of capitalism will simply make a small tweak. Matt will be playing Capitalist Whack-a-Mole for all eternity, because unlike classic Whack-a-Mole, the number of holes from which moles can emerge is not finite.
There is actually a mildly intellectually interesting philosophical question here, which is: "Is there a finite set of ethical principles that will yield a set of rules of capitalism whose cardinality is larger than the cardinality of the set of ethical principles?"
I suspect there is, but I also don't care, because I am a Humean, and I reject all clearly delineated ethical rules in favor of fuzzily defined, intuitive principles.