This is why even ideas like the nuclear family are hard to define or defend within Liberalism.
Remember that Black Lives Matter had on their website a declaration that they rejected the notion of the nuclear family.
Along the same exact lines the notion of what makes someone a citizen of a Western country is very hard to define or discuss. In some sense every person on earth is basically an American, they just haven’t been officially granted citizenship yet. No one can actually define what particular qualities qualify someone to become an American citizen or not, everyone just has vague notions and some ad hoc mishmash of various financial or political interests.
This makes discussions around illegal or legal migration in the West very difficult to have, purely on an intellectual level in terms of the categories.