Firstly, there are some things that should be disallowed irrespective of majority opinion. Raping people, for example. That's why countries have constitution-type documents that require super majorities to overturn instead of a simple majority.
Secondly, putting aside whether closed borders are in this category of things (I personally happen to believe it is), it unlikely that the economy can crash and refugees can 100x and we can get a right-wing populist who is also pro-democracy and liberal. Right-wing populists have consistently shown that they don't care about democracy -- they care about nation and empire and glory and race, not liberalism and not individuals. In fact, they hate liberalism with a passion. Look at how Orban has undermined the free press in Hungary. Look at how Trump has undermined confidence in US elections. Look at Turkey. And this is when things are prosperous. Look what happened after Russia's post-Soviet economic turmoil. We got Putin who threw away democracy the first chance he got. Hitler's popularity went up from the single digits to about 30% in 1 or 2 years into the Great Depression, mostly driven by the impoverished in rural areas. The Russian Revolution happened immediately after the extremely dire conditions post-WW1, leading the authoritarian Bolsheviks to take power. The CCP took power from the KMT in the context of poverty and humiliation resulting from British then Japanese imperialism (among other causes). It's causal, and it happens again and again.
Secondly, putting aside whether closed borders are in this category of things (I personally happen to believe it is), it unlikely that the economy can crash and refugees can 100x and we can get a right-wing populist who is also pro-democracy and liberal. Right-wing populists have consistently shown that they don't care about democracy -- they care about nation and empire and glory and race, not liberalism and not individuals. In fact, they hate liberalism with a passion. Look at how Orban has undermined the free press in Hungary. Look at how Trump has undermined confidence in US elections. Look at Turkey. And this is when things are prosperous. Look what happened after Russia's post-Soviet economic turmoil. We got Putin who threw away democracy the first chance he got. Hitler's popularity went up from the single digits to about 30% in 1 or 2 years into the Great Depression, mostly driven by the impoverished in rural areas. The Russian Revolution happened immediately after the extremely dire conditions post-WW1, leading the authoritarian Bolsheviks to take power. The CCP took power from the KMT in the context of poverty and humiliation resulting from British then Japanese imperialism (among other causes). It's causal, and it happens again and again.