We would be astonished at the number of evils that would vanish in short order, if the UN were eradicated in one simultaneous blow. All of their regional headquarters, all of their dozen-plus sub-agencies - all of it.
Take a close look at anything that we see wrong with the world, particularly the current problems besieging western civilization, and you'll find the UN at the core of the matter.
Those people are not just going to go away and leave us alone if we ask them nicely.