I sort of agree with this, as long as the wealth stays with a company and they keep reinvesting it it isn't a problem, it drives the economy. The problem arises when they sit on the cash or make huge payouts to stock owners(especially when these payouts ends up with a select few individuals), or when they buy off policitians.
I wasn't talking about a cap, not a hard one at least, what I meant was that if you earn $10 the tax is 0%, if you earn $50k it's more, if you earn $10B it's 98%. And yes the curve is exaggerated, I'm not trying to come up with exact numbers, merely give a rough understanding of what I mean.
The general idea is that the more you make the more tax you pay as a percentage of that income, but you also get to keep more in terms of absolute money because 2% of $10B is still more then 100% of $10. So there is still an incitement to make more money because even if the state taketh more of it away you still end up richer in terms of disposable money.