I claim that in all but the most obvious cases, you can't. It's a fool's errand, and thus the term "special interest" has no use but in propaganda. While used

I claim that in all but the most obvious cases, you can't. It's a fool's errand, and thus the term "special interest" has no use but in propaganda. While used in propaganda, I meant to explain that "special interest" == "not in the public interest". I agree that the latter is clearer.