Say you encounter someone, Sam, saying “I dislike [movement/theory/group G], because they say [bad thing B].” Say you’re a member/proponent of G, and you not only agree that B is bad, but you’re pretty sure that’s not representative of G, and indeed inconsistent with G, so you tell Sam that, and Sam replies that some other person Bob says B, and that Bob is a G. Under what conditions can we properly affirm that Bob is in fact not a G? In logic class we encounter the “no true Scotsman” fallacy:
“No Scotsman would drink vodka”
“McGregor [a Scotsman] drinks vodka.”
“Well, no true Scotsman would drink vodka.”
The illicit rhetorical move accomplished by this fallacy is to immunize a generalization against a refutation by counterexample by smuggling in an ad hoc modification to the definition.

But is every scenario like the one I’ve described an example of “no true Scotsman” fallacy? Say Bob claims to be a Christian, but frequently lies and betrays and kills. When asked, he reports that he does not believe in the divinity of Jesus, or even in God at all. So if Sam said “I dislike Christians, that Bob guy is just awful,” and you replied “look, Bob just is not a Christian, so you’re mistaken to dislike Christianity because you don’t like Bob,” would you be committing “no true Scotsman” fallacy? I think the answer is no. You are correct; Bob, despite calling himself Christian, is not one, and Sam is wrong both to take Bob as representative of Christianity and to dislike Christians on that basis.

This comes up in political contexts, of course. Sam claims to dislike libertarianism because he read something by Bob, who also claims to be libertarian, to the effect that it’s great that the police harass racial minorities and imprison them for minor offenses, or that immigration from Mexico is a bad thing because they’re mostly criminals anyway. This is a fictional example, but I’ve engaged on social media with people who claim that libertarianism is bad because that one guy is a racist, or that one other guy opposes immigration. I generally respond by enumerating the ways in which racism (or closed-borders or protectionism or what have you) just aren’t part of libertarianism. Am I committing “no true Scotsman” fallacy? I don’t think so. I think, as in the case of Bob the non-Christian, that there has to be a way to respond to caricature and distortion that is not also committing the fallacy. As with the religion case, Bob may simply be inaccurate in his self-description of his politics.

First of all, we might distinguish between (a) people who are academics, writers, attorneys, people who think about things enough to have what could even be considered a coherent set of views, and are libertarian, from (b) right-wingers (or whatever) who like 2 planks of the LP platform and then say they’re libertarian while nevertheless disagreeing with the other 95% of it. People in (b) are not coherent, and their self-labeling just cannot be taken for what libertarianism is. To act as though that is what libertarianism is is either unserious thinking, or deliberate dishonesty.

I can see how it might look like I’m doing “no true Scotsman,” but I am not. I’m saying that just because Bob says “yeah, I’m a libertarian,” that doesn’t mean that Bob is representative of libertarianism, and it might not even mean that Bob is libertarian at all (in the same way that he’s not a Christian). Here’s how: It’s possible that people can like something about a label, or what they heard that one time, that makes them think “that’s me,” when in fact they’re so misinformed that it really isn’t. This happens all the time – for example, lots of college-age people report a self-identification as socialist. On investigation, though, this turns out to mean they favor universal health care and free college, or are worried about income inequality, not that they want to abolish private property and nationalize all industry. So they say “I’m a socialist,” but in fact are not, because they don’t even really understand these theories well enough to have a coherent view. They’ve heard that free health care is socialist, and they want free health care, so they say they’re socialists. But if you give them some Marx to read, that’s not what they want at all. So too with libertarianism. Libertarians call for lower taxes, Bob wants lower taxes, so he says he’s a libertarian. But that’s obviously wrong if he simultaneously rejects the other 95% of what libertarians say. Bob is like the free health care kid in my analogy.

Of course, there are things libertarians disagree about, and in most cases it’s unhelpful to apply “purity tests” and excommunicate people. But if labels can mean anything anyone wants them to mean, there’d be little point in doing political theory, or philosophy at all, because nothing means anything, humpty-dumpty style. Socialist, fascist, libertarian, Austrian – we have to have some usage standards about when these words are deployed or we can’t really have any discussion at all. Most people are very confused about politics in general and labels in particular, so those of us “in the business” need to help promote clarity. It’s as if people debating medical issues said “hey, I say it’s virus, so just because you call it bacteria doesn’t mean I have to agree. It’s a virus to me”; or if people debating astronomy said “look, comets and asteroids are the same thing in my book, so I don’t care what you think the distinction is.” Nothing productive would come out of discussions like that.

We not only can help out by pushing for clarity and precision, we should do so. Whatever your political position, your cause will be poorly served by imprecision and humpty-dumptyism. I think it’s fine to claim that lots of self-labeled “socialists” aren’t actually socialists, and that lots of self-labeled “libertarians” aren’t actually libertarians. People’s self-claimed labels may not be accurate, especially in a world where labels are often a substitute for philosophy. It isn’t a “no true Scotsman” fallacy to point that out.