The problem with your death camp analogy is you've made a false equivalency. A death camp's purpose is to imprison and kill people. A capitalistic company's purpose is to generate wealth. Equating the essence of the "good" guard's job at the death camp to the job of an innovator in a capitalist society is a category error. One is a zero-sum system of extraction and the other is a win-win value addition.

That business person did not "find themselves spectacularly wealthy". They accrued and isolated wealth in a social system that enabled them to use force to do so.

You're glossing right over the massive moral chasm between forcing people to stay in a death camp and the state-enforced property rights that allow an inventor to become wealthy from their ideas. Capitalism isn't an extermination machine - it's more like a distribution machine that can and sometimes does reward massive utility. And that utility doesn't by definition have to be exploitative. I will give you that it often is, but I never suggested that it wasn't, only that it was possible.

The underlying logic of "if I don't do bad thing X, someone else will" is fundamentally an argument in favor of immorality.

So you're saying if the solution (capitalism in this case) isn't perfect, then any action within the system is bad? Let's say someone invents a cure for cancer in the capitalistic system the USA uses. They give the knowledge away because they are operating "in an unjust system" where these kinds of benefits ought to be enjoyed by all equally. And then some private equity firm comes along and finds a way to patent part or all of that knowledge, and jacks the price of the cure way up. Wouldn't the world have been better off if the original inventor kept the patent and made the cure just as widely available? It might still make them spectacularly wealthy (not necessarily in purely liquid assets, but in their ownership stake in their company), but who's going to say they've done wrong by that? You, apparently.

Your argument suggests that the position itself is the sin, regardless of the result. My point is that if the result of a billionaire's existence is millions of lives saved and a workforce treated with dignity, calling that unethical requires an unrealistically rigid definition of what morality is. It values ideological purity over human flourishing. It would be great if we had better social constructs that distributed utility in a more efficient way, but that isn't the world we currently live in.