If you have some vague general notion that equality is a good thing, and you believe that people ought to get approximately the same reward for an equivalent amount of effort, then a capitalist enterprise, in which a large number of people toil for a modest reward while the owner of the enterprise collects a far bigger reward, is morally indefensible.

I cannot fathom how any serious person could harbor such a belief, that reward should be simply proportional to effort, though it does lead to the widely-held conclusion.

No one wants to see someone who puts a lot of effort into planning a crime be rewarded. Nor should someone who expends much energy scratching their stomach expect to be paid handsomely. Wait, that's different they'll say, those are efforts toward ends which are not valuable. Well, who decides what ends are valuable? Is it not other people, who not only say they support the ends, but prove it by freely offering valuable remuneration to producers of goods and services?

I share your mistrust of ideology, but suppose we could do with at least a governing principle. I favor the society in which people can get ahead by asking themselves "How can I get what I want by giving other people what they want?"