> That's the problem with all these fallacies lists: things are a fallacy, except when they are not.

No, fallacies are always fallacy, but a fallacy is an error in logic that does not imply that the conclusion is wrong [0], only that the argument offered fails to establish the truth of the conclusion it seeks to justify.

[0] An argument for the negation of a conclusion based solely on a fallacy in an argument offered for that conclusion is the definition of the fallacy fallacy.