On the other hand I understand the principle that money makes more money (the principle of investment and ROI), and I don't see how "competitive market" tackles this.
It basically feels like the capitalism starts off from fairly-level playing field, but over time becomes more and more unstable, the gap ever-widening. We have already seen it fall (at the beginning of communist regimes), and I'm afraid we'll see it fall again.
That's a pessimist view, which I hope won't turn out to be true, but I'd be interested in exploring alternatives.
It doesn't address that because it doesn't make that argument, in that way. One of its starting axioms is that economy is a positive sum game. In the case of your statement, it might argue that (in the very general sense) money makes more money in a positive sum way -- more total wealth in the economy. Then to the latter it merely says that business that are better at making money (and generally, wealth) get to out compete those that don't. Its premise is it optimizes for wealth creation of the entire economy. I think that's the place to take the argument -- either that you fundamentally disagree with that premise or some outcome of it.
> It basically feels like the capitalism starts off from fairly-level playing field
Historically I don't think so. I"m not expert but read a lot and I'm currently under the impression that economies were historically locked down by government or tightly coupled government / mercantile entities.
WWII was a great leveling of the playing field. There are many times in history when Gini coefficients dropped precipitously. All the evidence points to the fact that wealth tends to accumulate in capitalist economies until crises or government intervention prevents it.
It's not a market problem. Even in a perfect market, a rich person would have most of its assets sitting or slowly moving, whereas a middle/working class person would spend their income.
So one gets the economy moving, while too much concentrated wealth stifles it.
Only if they're so inclined and even only part (they'll keep large parts in less risky form, including land etc -- also not sure how "investing" in "buildings in active use" is not rentierism and how it helps the economy. Whereas the middle/working class have no other option but to put the majority of their income directly in the economy again (buy things to live).
And that's not even taking into account the fact that the rich could very well invest elsewhere, or hide their money in tax havens, invest in foreign housing markets, and such, in which case the society they live in, and which they make their money, gets zilch of those money. Again, not the case for middle/working class people.
But assuming that the rich did invest most of their money, that would still have the problem of the rich calling the shots (through their investments and wealth), which is less of a problem in a less unequal society.
Edit: Love your name, love the reference.
The natural end of that is generally going to be prosperity across the board, and hopefully a government financially solvent enough to actually pay for those in need and essential services, all of which should be lower as a result of a better market doing much of that naturally.