This is 100% ad hominem, the fallacious kind. The validity of an intellectual argument in no way hinges on who makes the argument or why. Nice try though.
I didn't see any intellectual argument here. They were just describing his moral character. If it were 50% ad hominen you might have a point, but 100%, no, then it's biography.
The beginning of the article is the heavy lifting the author has to do to get his payoff at the end. The last two paragraphs are the payoff. This is classic 100% ad hominem. The beginning proves Milton Friedman is a bad guy and the conclusion is that modern libertarianism is flawed and invalid.
Here are the last two paragraphs of the article -- the point the beginning is supposed to justify -- with the key points bolded:
Like everything involving modern economics and libertarianism, it was a kind of giant meta-sham, shams celebrating a sham. Even the Nobel Prizes in economics awarded to people like Milton Friedman, George Stigler, or Friedman’s contemporary fans Heckman and Lucas, are fake Nobel Prizes — in fact, there is no such thing as a Nobel Prize in economics; its real name is the “Sveriges Riksbank Prize in Economic Sciences in Memory of Alfred Nobel” and it was first launched in 1969 by the Swedish Central Bank and has since been denounced by Alfred Nobel’s heirs.
And yet — in the words of Larry Summers, "Any honest Democrat will admit we are all Friedmanites now." Of course, there are no honest Democrats. And there are no honest economists. And these are the people who are framing our politics, the people who have told Greece and Spain they have no choice, and the people who today are making sure that the number one item on Obama’s and Congress’s agenda is cutting Social Security and cutting Medicare and cutting "entitlements" — and the only thing that divides the elites in charge of this mess is “how much of these moochers’ lifelines can we cut?”
The ad hominem formula is, basically, "because a particular person is a bad person or did some bad things, we can reject ideas he had or logical arguments he made". That is the overall formula of this article. Had he left out the last two paragraphs, it would be biography. With them there, the beginning sets up the conclusion.