Again, this whole 'tax the rich' bent you are on is off-topic. In fact, it seems you are not understanding utility in this context of marginal utility.

"It could be subject to the same utility if we taxed it, that's what I was getting at."

"Wealthy people aren't using money that society could put to great use."

Then you could say that the average person's 401k isn't being used either. But investments are a use of money that do contribute to society in providing capital to businesses and individuals. Gains on those investments are also taxable.

There are plenty of things we could do, but that's not really what we are discussing here.