Most libertarians - and even many conservatives - believe a nation can stand if its laws/mores/principles are merely neutral. Go figure.
But what about those who want to impose the opposite and will do so when they have enough population to do so.
Unlimited immigration is a libertarian goal, that means that American law/mores/prinicials will become whatever the third world colonists want, if sharia law is desired, then sharia law it will be.
Don't be naive about things like Islam and the conquest of the world through immigration, and operating within the system at first, changing the system as much as they can, and then becoming the system.