I'm a big fan of aggressively progressive tax systems but it isn't as simple as you think.

California has a very progressive tax system, with most people paying some but most of the money coming from a small number of taxpayers. Sounds great, and basically most people like it. The problem is that when the economy tanks, California takes a huge hit in income since wealthy taxpayers' capital gains drop precipitously.

Yes, there's a simple-to-describe fix: build a surplus in good times and borrow in downtimes. But this is very hard to implement.