Let's review Obama's own words about that time, from Dreams from My Father:
To avoid being mistaken for a sellout, I chose my friends carefully. The more politically active black students. The foreign students. The Chicanos. The Marxist professors and structural feminists and punk-rock performance poets.So where are the fallacies again?
McCarthy writes:
Yes, Ayers is blunter than Obama. As he so delicately told the Times, America makes him “want to puke.” The smoother Obama is content to say our society needs fundamental “change.” But what they’re talking about is not materially different.
But "change" doesn't necessarily mean "fundamental change." Most politicians who promise "change" rarely bring anything very sweeping. And saying you are for "change" isn't the same thing as saying that America makes you "want to puke." That's just a cheap shot.
The other problem is that the Eighties were a very different time from the Sixties. Kids who read Foucault and Derrida and Said, even kids who protested nuclear power or apartheid, weren't quite the same as the (literal) bombthrowers of fifteen or twenty years before.
McCarthy may be right about Obama and Ayers, and Obama's associations make one question his fitness for the presidency, but most of those "Marxist professors" in the Eighties were more concerned about getting tenure than making revolution, so it's not easy to know just what to make of Obama's comments in his memoir.