Thanks for the, as always, great post. You start by asking:
First, if it’s very uncertain how tax policy is going to affect innovation, why does that imply that taxes on the wealthy should be low?
I did not argue that that premise implies that conclusion. Krugman made an affirmative claim (or, as I went into in the post, he used language that Ozimek showed, I think correctly, could only be interpreted reasonably as implying) that innovators capture materially all of the economic value that they create. Ozimek provided a thought experiment that shows that this seems to violate common sense. Common sense is sometimes wrong, but I think the burden of proof is on those who make an affirmative claim. Krugman doesn’t provide any evidence for his claim beyond waving his hand at “textbook economics,” and Ozimek called him on it. I applauded this.
My only addition was to make an observation. Krugman claimed a contradiction between the belief in free-market principles and the belief that innovators can create material economic value that they do not capture, because the textbook economics that he believes is the foundation for belief in free market principles also claims that workers will capture the economic product of their labor. In fact, at least some people who hold free-market principles (e.g., me) do not ground their beliefs in Krugman’s textbook economics. So I am free to simultaneously hold the beliefs that innovators often cannot capture the full value of their work, and free markets are a good general organizing principle for the economy, without (at least this specific) contradiction.