The original comment ("In theory, yes. In practice, no.") is from ad hominem. It does not provide any actual thoughts or arguments, it simply says that there is

The original comment ("In theory, yes. In practice, no.") is from ad hominem. It does not provide any actual thoughts or arguments, it simply says that there is an economist that thinks this way, implying that it should be enough of a reason to trust it. There was no argument except for ad hominem! Of course the response to that can only be a defusal of such argument.