But here’s where competitive markets come in. In a perfectly competitive economy, with no monopoly power or other distortions — which is the kind of economy conservatives want us to believe we have — everyone gets paid his or her marginal product. That is, if you get paid $1000 an hour, it’s because each extra hour you work adds $1000 worth to the economy’s output.

In that case, however, why do we care how hard the rich work? If a rich man works an extra hour, adding $1000 to the economy, but gets paid $1000 for his efforts, the combined income of everyone else doesn’t change, does it? Ah, but it does — because he pays taxes on that extra $1000. So the social benefit from getting high-income individuals to work a bit harder is the tax revenue generated by that extra effort — and conversely the cost of their working less is the reduction in the taxes they pay.

Or to put it a bit more succinctly, when taxing the rich, all we should care about is how much revenue we raise. The optimal tax rate on people with very high incomes is the rate that raises the maximum possible revenue.

And that’s something we can estimate, given evidence on how responsive the pre-tax income of the wealthy actually is to tax rates. As I said, Diamond and Saez put the optimal rate at 73 percent, Romer at over 80 percent — which is consistent with what AOC said.

An aside: What if we take into account the reality that markets aren’t perfectly competitive, that there’s a lot of monopoly power out there? The answer is that this almost surely makes the case for even higher tax rates, since high-income people presumably get a lot of those monopoly rents.

So AOC, far from showing her craziness, is fully in line with serious economic research. (I hear that she’s been talking to some very good economists.) Her critics, on the other hand, do indeed have crazy policy ideas — and tax policy is at the heart of the crazy.

You see, Republicans almost universally advocate low taxes on the wealthy, based on the claim that tax cuts at the top will have huge beneficial effects on the economy. This claim rests on research by … well, nobody. There isn’t any body of serious work supporting G.O.P. tax ideas, because the evidence is overwhelmingly against those ideas.