To justify Bitcoin specifically you'd need to explain why it in particular should be the one-and-only (or at least, one of a fixed and finite set). A government could do it by fiat, and it wouldn't surprise me to see a government bless some cryptocurrency as its default transaction mechanism. A stablecoin could do it by piggybacking off a government fiat.
It's not impossible that the population as a whole could simply land on Bitcoin, much the way a government exists by the collective consensus of the people living there. But I don't see that as being very likely, since there are too many alternatives. It has the first-mover advantage and might just succeed, but I consider other cryptocurrencies more likely.