Colin, Scott and I are working on a paper for the Ontario Society for the Study of Argumentation conference on the problem of subjunctive inconsistency, or, as we term it, subjunctive tu quoque arguments.  The idea was originally Colin's (see here).  In a very basic sense, the argument scheme goes like this:

you hold belief x or perform action y, but under different circumstances, you would reject belief x or condemn action y.

This is basically an accusation of hypocrisy, even though in this case the hypocrisy is completely hypothetical.  No one is claiming that the accused is actually a hypocrite; merely that the accused would be a hypocrite were the situation different.  This might seem odd at first blush (whoever heard of a subjunctive hypocrite?), but it's fairly common, so much so that we have phrases for this kind of judgment: "don't judge a man until you walk a mile in his shoes" or "in my place you'd do exactly the same thing."

I ran across an example of the mishandling of this sort of argument in Stanley Fish's blog column.  He writes:

In a recent column in The Miami Herald, Leonard Pitts criticized Mississippi Governor Haley Barbour for failing to denounce the proposal to honor Ku Klux Klan founder Nathan Bedford Forrest by issuing a vanity license plate bearing his name. When pressed by the NAACP, Barbour said, “I don’t go around denouncing people.”

“Presumably,” Pitts retorted with obvious sarcasm, Barbour “would be equally non-judgmental if his state were to consider similar honors to Osama bin Laden, convicted spy Robert Hanssen or Columbine killers Eric Harris and Dylan Klebold.”

Pitts' charge is exactly an ad hominem tu quoque subjunctive variety.  But this puzzles Fish:

Just what is Pitts demanding here? He is demanding that Barbour earn his right to be non-judgmental with respect to Forrest by being willing to extend the same generosity to bin Laden, Hanssen, Harris, Klebold and literally thousands of others. You can withhold judgment in this instance, he is saying, only if you would also withhold judgment in all arguably equivalent instances. What Pitts is urging (implicitly) is not the condemnation of Ku Klux Klan founders, but the principle that condemnation or the withdrawal from condemnation must be evenhanded. You get the right to say something critical of what someone of the opposite party said or did only if you would be similarly critical when members of your own party said or did something similar. And you get the right to refrain from criticizing some only if you will also refrain from criticizing others.

This is a familiar move in political argument (it is related to the tu quoque, or “so’s your old man” move). We saw it in spades a while ago when Democrats lamented the incivility of public discourse and blamed right-wingers for proclaiming over and over that President Obama was a foreign Islamic usurper working to undermine American values. The right replied by rehearsing the litany of things said by democrats about George Bush — he was a tool of corporate interests, a warmonger and an enemy of civil liberties. So what gives you the high moral ground, those on the right asked, when you were equally vile in your accusations?

I think Fish's description of the logic is right on the mark.  Pitts' charge is a tu quoque.  The problem, however, is that not all tu quoque arguments are fallacious.  This one, I think, is one of those cases.  Fish doesn't get this.  Skipping several paragraphs (where Fish wrongly alleges that subjunctive tu quoque arguments are instances of the liberal tendency to favor process over content):

Leonard Pitts thinks that the Klan and its views are beyond the pale – “a man who betrayed this country, founded a terrorist group and committed mass murder is a man unworthy of honor” — but he also thinks – this is his mistake — that it is an argument against the honoring of the Klan’s founder that Haley Barbour would probably not give Osama bin laden the same benefit of the doubt he seems willing to give to Forrest. (Of course, Barbour is just playing the familiar game of political equivocation.) To which I say, what does Osama bin Laden have to do with it? Bringing him and the other symbols of wrongdoing in just takes the pressure off the core moral question — was and is the Klan evil — and turns it into a question of formal equivalencies. (Are you also willing to be fair to . . . ; the list is endless.)

At bottom, Pitts’s case against honoring Forrest is that he was a bad man dedicated to realizing a bad cause. Just say that, and don’t mess it up (and dilute it) by playing the “gotcha” card, by challenging Barbour to display his liberal bona fides and accord equal treatment to everybody. That’s not what the moral life is about.  

Fish is wrong about the motivation for Pitts' claim.  It's not a matter of alleged liberal fairness or obsession with process over content–Fish is just confused about that. We might put it something like this:

Bedford Forrest was a racist murderer, honoring him would be like honoring Bin Laden, and I'm certain Barbour wouldn't want to honor Bin Laden. 

Pitts' subjunctive tu quoque argument highlights, rather than obscures, the relevant moral issue: Forrest was a traitor, racist, and terrorist; honoring him is like honoring Bin Laden, so for this reason, Barbour ought to honor Bin Laden.  But Barbour wouldn't honor Bin Laden, therefore, etc.  In other words, Pitts isn't avoiding making a moral argument by hiding behind process (whatever that means) or playing "gotcha," he's making a moral argument.