Another day, another idiocy comes spouting out of the mouth of that neo-liberal shill Mankiw. No wonder he has to disable comments on his blog.
As anyone who knows (real, not fake) economics and is willing to rub two thoughts together will be able to tell you, Mankiw's argument is a sham. It's a complete strawman because progressive income tax is based on a concept of equality of outcome. And another little concept about the differential moral utility of money. These may be concepts that Mankiw scorns and wishes didn't exist (he's certainly trying to ignore them) but they do.
So when Mankiw assumes that taxing "entrepreneurial genius" (whatever the fuck that means) is the same as taxing entrepreneurial outcome, he is being a lying whore and a two-faced duplicitous son of a bitch.
That's because taxing "entrepreneurial genius" is all about equality of opportunity and not equality of outcome. Taxing "entrepreneurial genius" is also neutral towards the differential utility of money, something progressive taxation is not since the whole point of it to change people's behaviour. In other words, the two types of taxation are violently opposed.
And despite the fact Mankiw casually treats taxing "entrepreneurial genius" as an acceptable stand-in for taxing revenues, he knows the two aren't equivalent because he prefers taxing opportunity. That's because, as any good shill must, he doesn't like taxes that affect people's behaviours but believes taxation should let criminals be criminals.
As a moral person, I violently disagree with Mankiw's amoral prescriptions. As a systems designer, I violently disagree with needless duplication (between revenue-generation and moral incentives). So I vastly prefer taxing outcome and not opportunity.
Finally, as a dissident, I despise a lying shill like Greg Mankiw.
It is a testament to the utter depravity of mainstream economics that nobody has yet stood up to throw egg into Mankiw's smug lying face.