Yes, you need to tax where the money is. On the poor and middle class.
Wait... what? Why? Because there are so many more of them by far.
It is a lot easier to get one dollar out of 300 million people, than it is to get 300 million dollars out of one person. That one rich person has the ability to fight back more effectively, and they are a lot more likely to notice the fleecing and try to do something about it.
More to the point, there are not a lot of people you can get 300 million out of. Even if they don't all flee to the Bahamas, you start to run out of rich people.
The Communists in Russia and China killed all the rich people and took their assets and money. It probably helped a little at the beginning, but it clearly didn't fix their problems. If you add up the amount of money that the richest people in the US have, and then take *all* that money away, including their assets and capital, you get about a trillion dollars. Sounds like a lot, but the US goes through that in about three months, every year. After you spend all the rich people's money, you then have the same expenses, but you've done little more than add a handful of people to the welfare rolls.
A small number of phenomenally rich people doesn't compare to the amount of money that millions of workers make put together. And those rich people aren't holding on to that money in the Scrooge McDuck vault. Unless they reinvest their money, it gets taxed by inflation. Not to mention that most of the "wealth" of people like your Bill Gates' and Buffets are in corporate stocks and other investment instruments, not in actual cash.
The problem with the economy isn't that there are a lot of rich people hoarding all the money, it is that our spending is out of control and that the poor and middle class are facing increasing prices without increasing wages.
If there is a problem with rich people, it is not so much that they are extremely rich as much as that it causes them to lose touch with the basic need to survive, which causes them to become involved in decisions that benefit only them, while ignoring the human element. They are not a giant money pinata which if we keep hitting it, will make everyone and the government suddenly comfortable, the biggest problem with the rich is that they *make the decisions for everyone* because they have the ability to sit around and run for Congress, or contribute to campaigns, whereas the rest of us need to get a real job.
In short, you have people running the country that don't understand the actual problems that most of the country has.