It has been my observation that it is not that only people of unscrupulous character become wealthy, but wealth tends to make you progressively more unscrupulous, i.e. not care about anything but yourself and your family unless you are legally compelled to do so.

In my mind, I've come to call this relative wealth toxicity. We all know of power toxicity (power corrupts). I think wealth has a similar effect on human psychology. The "relative" part is because a modern-day middle class person is, in absolute terms, is wealthier than a medieval lord, but do not behave like one. It is the relative power and the rarified social status that wealth brings, that results in the toxicity.