> This is a true Scotsman’s fallacy. “Legitimacy” of self-interest is fluid and subjective

Legitimacy is the "alignment" question. We can't objectrively judge it, fundamentally, because it's an expression of values: to what degree do the society's system of incentives align with the greater good?

That isn't a No True Scotsman's fallacy, because there are true Scotsmen. Literally Scotsmen. And every other member of a complex society. Including, in all likelihood, you, a person who subjects themselves to laws and employment and fielty for reasons that are a mix of duty and self interest.

You seem to fail to grasp that just because people answer the call to duty it does not mean the duty is aligned with their self interest. The most stark example is joining armed forces.