On the other hand, it increases the wealth of individuals. Now, that wealth isn’t used for them to live in decadent splendour. No, no, no. The idea is that they’ll channel tax savings back into the market through wise investments.

This is a gross misunderstanding of "Trickle down." There is no assumption about reinvestment. The assumption is that the rich will spend their money on decadent stuff. When Larry Ellison buys a gazillion dollar yacht, he does not build it himself. Ordinary people build it. That's why luxury taxes always backfire - they put the people who make luxury goods out of work. So the real issue is the social utility of the things people make, not the economic effect of rich people buying them.

But it's not as if there isn't enough investment capital to go around. The rich are reinvesting. For the most part, the rich aren't really taking their wealth out of their companies. Their wealth consists mostly of market value, not cash. So, maybe what we should be asking is what percentage of spending is done by the uber-rich. Whom are they pricing out of what market? What must I do without because Jeff Bezos is rich as Croesus? That's hard to answer, considering how much money I save by spending in the very way that makes him so rich.

The irony is that we are actually living through a period of trickle-up economics. The super-rich are making their fortunes by selling huge volumes of low-cost goods and services to more and more people. It's because so many people can afford so much that the purveyors are so rich. It wasn't always thus, but the arc of economic history (to borrow shamelessly) bends toward distributive justice, not in terms of wealth, but in terms of access to goods and services. And at the end of the day, that's what economies are for.