100 CEOs Have as Much Retirement Savings as 116M Americans

I have more money than every person in the US who has $0 to their name combined.

This metric isn't useful for anything other than shocking headlines.

And in 2004, the Democratic Party ran a billionaire for President. Whoopie-doo.

Who does it serve? Using other peoples money might allow you to grow your business faster improving the economy. I might agree if you divide it by industry, oil and gas mining or finance has a higher rate.

Long term capital gains tax is 15%. Interest on simpler accounts are taxed at a higher income rate. This is a very loose interpretation of what you're asking for, but with lots of side effects. Like people who trade their labor for income are taxed at a relatively high rate, while people who sit back and collect rent on capital "risking their money" are taxed at a fairly low rate.

At high concentrations of capital, the "risk" is not so much a risk. (esp when the full force of the gov't is backing many aspects of the risk...)

How would you define risk free investments? Buying Walmart stock and holding it for a decade? Buying a house and renting it out? Lobbying for preferential treatment for a business/sector you have a large stake in?

The latter is obvious a problem, but if you can define that process legally then you could just outlaw it outright instead of trying to penalize it with taxes. Any investment I can imagine that is close to risk free is either already illegal or technically illegal but hard enough to define that people can skirt around the edges of the law.