Unfortunately, many Introduction to Philosophy students leave with several misconceptions about the nature of fallacious reasoning.  They draw the conclusion that fallacies are a kind of negative guide to reasoning.  For instance, never attack the person, as such attacks break the ad hominem rule.  Another misconception is that calling something a fallacy is sufficient for dismissing someone's position.  That's an ad hominem, therefore, etc.  Unfortunately, some–even some professor types–seem to think this characterizes the entire field of inquiry into fallacious reasoning: when fallacies are discussed, they see a kind of juvenile name calling in place of honest and fair analysis.

Sometimes, however, that's the case.  This, for instance, would seem like a reasonable accusation of an ad hominem:

All of which brings us to the distinctly Greenwald parts of the book–Greenwald takes an unseemly relish in engaging in irrelevant personal attacks. Personally attacking Ronald Reagan at least makes sense on some level. But personally attacking private citizens with different ideologies has a certain senselessness attached to it.

But no.  The relevance of "personal attacks" depends on the conclusion drawn–not on the object of the attack.  Personally attacking Ronald Reagan makes sense only when the "attack" draws a conclusion relevant to the attack.  Reagan's personality is no more relevant in the grand scheme of things than that of any private citizen.  While we expect a politician to be subject to such attacks, those attacks aren't more justified on logical grounds.

This is especially the case when the question concerns hypocrisy.  Al Gore is not a hypocrite for driving a car, unless he says "don't drive a car."  He says, "Climate science says x, y, and z."  Whether he drives a car is separate question.  His driving a car has nothing to do with that particular argument.  Now, when someone calls someone else a moral degenerate who should not be trusted, you're going to reasonably wonder about the purity of the accuser–to do so doesn't make you any less of a degenerate, all things considered, but it the credibility of the accuser is certainly relevant–insofar as his accusation rests on his credibility.  Continuing from above,

Even if every reader of Great American Hypocrites walked away from the several pages that attack Norman Podhoretz (to take just one of the many conservative thinkers that Greenwald assails) convinced that Podhoretz is just about the most awful person to ever walk the face of the Earth, Podhoretz's ideas would remain unscathed. Podhoretz has never argued that a reader should agree with his ideas because he is such a wonderful guy. Instead, the ideas have a life of their own.

Greenwald's own success makes his personal attacks particularly ironic. There was nothing in Glenn Greenwald's background that suggested he should have been one of the kings of the progressive blogosphere. And Russ Feingold didn't read passages from Greenwald's first book from the Senate floor because Greenwald is such a fine human being. Greenwald gained prominence because of the power of his ideas and his writing. Whatever prominence he retains will also result exclusively from the quality of his work. It's a mystery why he doesn't realize that it operates the same way at all spots on the ideological spectrum.

Great American Hypocrites will likely be a big hit. Whatever the equivalent of red meat is for the angry left, this book is it. As a confessed Greenwald admirer, I found it largely disappointing. Like the rest of us, Greenwald has both strengths and weaknesses as a writer. Too much of Great American Hypocrites indulges his fondness for pointless ad hominem attacks, the weakest aspect of his work.

Many of Greenwald's fans will probably take delight in his description of Rush Limbaugh as a "draft-avoiding, illegal-pill-addicted and multiple-divorced (man) burdened with one of the most decadent and degraded lives of any public figure anywhere." Whether they take note of the irony that a mere two pages later Greenwald decries our "attack-based personality-obsessed politics" is an open question.

If Greenwald himself sees the irony, he doesn't betray any such awareness in "Great American Hypocrites."

It seems facile to accuse someone of hypocrisy for accusing someone else of hypocrisy.  That succinct and true description of Rush Limbaugh, in other words, is not a fallacious ad hominem unless Greenwald uses that as evidence to dismiss views unrelated to Limbaugh's character–or the moral character of those whose positions he advocates in the course of making those attacks.  But that, I take it, is not Greenwald's point in writing a book about hypocrites.

It always depends, in the end, on the conclusion you're drawing.  If you want to malign John Kerry's manhood (as Limbaugh did) by way of supporting Bush as the alternative, then Bush's comparative manhood is a relevant question.  That, I take it, is Greenwald's point.  But I'll leave that to him.