Life isn't fair but the legitimate purpose of government policy is to shape society in the ways people want it shaped. Otherwise we'd just have a monarchy and say "Life isn't fair." (And it is worth remembering that the people can always revolt and slaughter the rich who don't like their policies, that's a legitimate way of establishing a government.)

I'm a fan of saying, first, that people did not earn their money past a certain point (my income has more than doubled since I entered tech and I am certainly not working more than twice as hard, I just joined a hedge fund instead of an unprofitable startup, and as a result I am firmly comfortable with any of these high tax brackets affecting me personally). Then you can say, we'll tax much more heavily at the point that you don't need the money to live. Then you simply don't accumulate the money needed for your children to live off passive income, and the question doesn't arise.