"Most desirable" is subjective, and a simply being native to (or residing in) a region, as opposed to conducting structure study of the relevant domains, is not particularly likely to provide any deep insights into what cultural patterns are more desirable to reform (or even on the objective questions that precede the subjective "most desirable" question of which cultural patterns are more amenable to reform and what the effects of attempts to reform those patterns would be likely to be.

> It's also possible that Studwell does not entirely have the region's best interests at heart, and is writing to influence things in his favor.

The same would be true of natives, who are quite likely to make recommendation in their own perceived personal interest whether or not they are in the general interest of the population of the region. On the objective questions of effects, that's what you use reason and analysis of presented evidence, rather than evaluation of origin of the author, to evaluate the arguments. What you propose is adopting the ad hominem fallacy as a preferred system of judging arguments.

> After all, that's why the USA doesn't allow people born in other countries to become President.

The USA allows people born in other countries to become President, it doesn't allow people not US citizens at or by birth to become President.

And the history of the relevant clause does not provide much evidence of any particular basis for that restriction; any such explanation is purely speculative.