This is a bad idea, as it will incentivize them to leave the country, to where there are lower taxes

Increasing taxes one people is not the way to eliminate the deficit, the way to do it, is through less spending and more profitable and progressive economic choices. However, there should be some form of limit to the amount of money any individual has, because we do not want to live in an oligarchy, and being a multimillionaire is excessive, but since it will never get enforced properly, it is maybe a bad idea.