[Grue3]

On the contrary, this fallacy is very important and applicable. Without it you cannot criticise any group G on the basis of X when a member of this group happens to declare that "I'm not X and anyone who is X is not a member of G". This is seemingly a perfect defense as long as there's a single member who is not X.

It's important to call out this fallacy, because the membership in a group can't be defined on the basis of a person's conduct, since there's no way to monitor that every member of the group adheres to this conduct. Therefore you can't know if anyone is a member or not unless you watch this person 24/7. There must be a different way to assign membership. A membership of most religions is decided on the basis of self-declaration. A membership in US Army is decided on the basis of application and being approved by the powers in charge. For example if US Army has a tendency to employ rapists, it's valid to criticise US Army for this fact even if they have a rule that forbids such behavior. If self-declared Christians tend to persecute and kill people in the name of religion, it's valid to criticise Christianity for this behavior.

[notdonspaulding]

    > On the contrary, this fallacy is very important and applicable.

I don't claim that it's an unimportant fallacy to understand and recognize and apply. Instead I said it was my "least favorite", because of it's so rarely applied correctly. By the rest of your comment, I get the impression you didn't catch my meaning.

    > For example if US Army has a tendency to employ 
    > rapists, it's valid to criticise US Army for this fact 
    > even if they have a rule that forbids such behavior.

Here, the critical point is not that the US Army employed a rapist or even several rapists. Instead you're saying they have a tendency to employ racists. No True Scotsman would only apply if someone from the Army made a statement in complete denial of that fact, hand waving it away by pointing out the rule and saying something to the effect of "The Army has a rule against rape, so anyone who does that isn't a real soldier". It's a valid No True Scotsman because the behavior is clearly evident in a non-fringe component of the group.

If someone did make that statement in sincerity, sure, send in the No True Scotsman patrol and take 'em out. But that's not how it usually happens. Typically, there's a singular incident. That's often followed by a careless article which paints with an overly broad brush: "Does the Army have a rape problem?".

And that is the point where I start looking for the misapplied No True Scotsmans to crop up. There's no way for anyone to defend the Army by pointing out that it's against the rules, or that the number of rape incidents in the army is lower than the general population, or really any other facts.

    > It's important to call out this fallacy, because the 
    > membership in a group can't be defined on the basis of a 
    > person's conduct, since there's no way to monitor that 
    > every member of the group adheres to this conduct.

I believe this idea right here is the source of all these misapplications. And it's just false. Of course membership in a group can be defined by a person's conduct. Try comparing Hacker News to Reddit in 3 or 4 comments and see how quickly you get shadowbanned. In fact, I'd say defining group membership based on conduct is the rule, not the exception.

No True Scotsman is intended to point out the fallacy of someone inside a group avoiding criticism by constantly shrinking or changing the group rules in order to draw a distinction from some negative person or incident. If the goalposts aren't moving, then its likely the person really isn't a True Scotsman, and you should maybe try to understand why not.