You gotta be careful of the Laffer Curve[0] though. Tap into the rich too much and they'll leave. Make it illegal to leave... well, your country is going downhill fast.
The exact value is near impossible to pinpoint, but you can find it by gradient methods. One thing for certain is that it's lower than the rate I currently pay. ;-)
the laffer curve and supply side economics is junk/propoganda masquerading as economics. It's about as real as the scientific studies exxon releases against global warming.
We should tap into it on a global scale. We'll have Moon colonies in no time!