I’m not going to dismiss this concern out of hand because I feel like it’s a good faith argument. But perhaps we can think a bit farther outside the box. Now, capital is always going to be required for economic activity to take place. Agreed. But I don’t think that whoever manages the allocation of capital needs to be compensated above and beyond what any other laborer doing an equivalently technical job needs to make. And they should be paid for the labor, not for the leverage they have as owners of capital.
How that is to be accomplished is.. complex. But that’s definitely the goal. But let’s not assume that we need some class of people who have the privilege of being the owners of capital.
Here's a tool that increases productivity. There are three people who need to get paid: the tool maker, the one who buys the tool, and the worker who knows how to use the tool. (The worker should be more productive with the tool, and therefore worth more than the worker who does not know how to use the tool.)
If you're saying that the one who bought the tool and the worker who uses the tool should profit equally from the tool, I might agree with that. (I'm not sure; I'd have to think about it some more, but it's not a clearly wrong position.)
Now here's someone richer than that. He buys two of the tools. If you say he should get as much as the worker for the first tool, and as much as the worker for the second tool, again I might agree. If you say he only gets as much as any one worker, no matter how many tools he buys, I disagree. I even think that you should disagree, for selfish reasons. We need these people to buy the tools for the overall growth of productivity. If we have to bribe them with returns on their investment, so be it. (The alternative is that the rich person only buys one tool, and then stops, because they would get nothing from buying the second tool. That may feel good, in that it doesn't let the rich earn more than anyone else, but it doesn't help grow the economy. And growing the economy is the only way that there's actually more for people, as opposed to simply dividing the existing pie in a different way.)
How that is to be accomplished is.. complex. But that’s definitely the goal. But let’s not assume that we need some class of people who have the privilege of being the owners of capital.