If you believe in a massive and active military, militarized borders and restrictive immigration policies, support for law enforcement as they currently exist, traditional family values, and the need to preserve a national culture, you’re not a libertarian. You’re not fooling anyone. You want a highly ordered and hierarchical society enforced by state coercion, just give us all a break and stop pretending like your beliefs about taxes and firearms make you a freedom fighter
Way I think this argument is justified by those types is that because we don’t have Freedom where businesses or even towns are allowed to discriminate, the government needs to do it instead.
To me that result has a very different takeaway though.
While OP has a point, there’s also the issue that Libertarianism has to have political support (including within that culture) in order to be maintained, and mass migrations can change the political environment of a territory pretty substantially.
It makes more sense if you assume it’s fragile rather than the default to which all societies will gradually slide.