To be clear, I'm not describing this as legitimate self-interested conduct. Elections are an alignment mechanism. Stiff penalties for corruption another. We don't have the latter in America.
Which means self-interest and collective interests are often at tension rather than alignment.
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.