It is an excellent post. The first part deals with Robert Frank, the second part deals with the recent Diamond and Saez paper, excerpt:
Finally, I have no idea where that “behavioral elasticity” is coming from, and I don’t trust it. My best guess is that it includes none of the factors that I think are important in addressing the problem. What we need here is a dynamic general equilibrium model that can take account of the short run and long run effects of a change in the income tax schedule. My best guess is that “behavioral elasticity” means that Diamond and Saez are measuring the effects of tax evasion and the intensive margin of labor supply, and that’s all. If so, I think they miss most of what is important:
1. There’s also an extensive margin. Tax people at a higher rate, and some drop out of the labor force.
2. Taxes affect occupational choice. Some work by Manuelli/Seshadri/Shin says that the effect of taxes on human capital is big time. Why do I want to undertake a costly and risky investment for a very small payoff?
3. Entepreneurial activity has to be very elastic with respect to tax rates at the top end. Why would I want to risk my own wealth or that of my close family for a very big payoff with very low probability, if that big payoff is taxed at 73%?
4. The United States is highly dependent on highly-skilled labor that migrates here from other countries. With a top tax rate of 73%, the Indian engineers might prefer to work in India, and the Canadian professors might prefer Canada.
Thus, I think it is likely that tax revenue is much more elastic with respect to the tax rate, particularly in the long run, than Diamond and Saez are letting on. To evaluate this properly, you need a serious model, and they have not provided one.