If we could just close the loopholes, bar lobbyists from Washington, or at least ameliorate their successes, it would go a long way towards the cliche "pay their fair share."

I understand the concern that the wealthy would flee were they to be taxed what they would consider to be unfairly.  Where would they go that they wouldn't be treated less fairly eventually than in the United States?  Find an Atlas Shrugged safe haven that eventually would cave in on them.? 

For example, I can see a company leaving France for the US, but not the other way around.

I've often thought about an economic NATO, where tax rates would be universally regulated among its members, barring the temptation to move to a better place.

Problematic is that the wealthy assume wealth brings automatic expertise in any subject.  They waste millions in foundations designed in the first place to justify their greed.

As I've written before here, I revulse when billionaires profit from the progress of civilization by filling in the next blank

But , in the end, you're right:  Just a little movement towards fair play.