I think Joe just made up that argument and probably has no facts to back it up. I know of numerous economists who think high marginal income tax rates are job killers. Here's an example of some of this economic research: The Small Business Tax Hike and the 97% Fallacy
http://online.wsj.com/article/SB10001424052748703959704575454061524326290.html?mod=WSJ_Opinion_LEADTop
Link to this editorial here:
I've been trying for some time to revive the discussion of margin.
On the capital side, raising the rate on the high end discourages further growth, (especially on top of other regulations). The best example I can think of is how certain laws apply to companies with 50 or more employees. If you have 49, you sure are going to think long & hard about hiring #50.
Marginal effort applies on the low-end, too. Poor people aren't stupid. Why work at minimum wage when it's not that far from the bennies from not working at all. (and it gets even worse when one considers double-dipping and other fraud).