Is "the rich getting richer" a problem?

[Baalzamon]

Lafiel said:

yea the problem is money has gravity, it atracts more money

market regulations and taxation has to keep that in check, because too much money accumulating on some few individuals is bad for the rest

Why is that bad for the rest (Outside of the fact that money buys corruption)?

People say stuff like this all the time, but can never provide any definitive proof.  Prove to me with a definitive argument that people are legitimately worse off when money continues accumulating more and more on a select few (which is actually quite a bit...1% is 3 million Americans).  Prove to me that without this money as it is now, people would somehow be better off.