Of course. Not that I agree with that idea, but no one should give up the wealth that they built up without sufficient guarantees (and the guarantees need to be enormous) that everyone else will and that it will be used for the greater good. For example, in Western Europe after WWII such taxes could be raised effectively. Right now, governments have more of a trust issue to effectively make policy like the above. But being impractical does not imply it is a bad idea as of itself.