By far the most interesting critique of capitalism (in the libertarian anarchist sense) to me is that it constitutes a sort of luck worship: the premise of property rights is that barring aggression, people deserve whatever they have; whatever they can get. In other words, barring aggression, whatever happens naturally is just; luck (or a combination of luck and intelligence) determines who's entitled to what; might makes right.
To my own disappointment, of all the communists I've debated, I've never heard this argument. It came to me entirely on my own.
If we believed, as one might intuitively want to, that luck never affects what anyone's entitled to, we would discard the entire concept of homesteading and essentially believe in redistributing wealth so that everyone gets what they deserve (Chaos Anarchism).
Despite how much conflict this would cause (which isn't a reason for rejecting an axiology - that would be an appeal to consequences), such an ideology of perfect meritocracy (or equality if you're not as big on the merit factor) makes sense. It's attractive in exactly the same way as argumentation ethics.
And yet, this ideology is undeniably wrong, and for no other reason than that it doesn't match my conscience.
I can make the simplest, strongest scenario to prove how clear it is: Alice is chased by a bear and Bob could make the bear chase him instead. He doesn't; he chooses his own life over Alice's. Few people would claim this is immoral, and those that would (mostly Christians) would still find it a minor sin at worst. Then the other version: it's Alice who has the power, and she chooses to make the bear chase Bob instead. This one is obviously murder. We just can't honestly deny that there's a massive difference. There's no avoiding the conclusion that, even if you don't put it this way, Alice is less entitled to life because she's the one who would naturally die here.
To judge the two as morally equal, you would have to have let logic distort your mind to exactly the same extent as Ancaps have to to claim you couldn't steal a small amount to save a life.
And that, if you ask me, is the proof that people deserve what they naturally get. That luck deserves respect, albeit not as an absolute. If it's undeniably true despite seeming counterintuitive, it must be a prime value.