Libertarians are intrinsically and on principle cowardly and hedonistic loners who will not suffer privation, take risks or undergo personal suffering either for the good of the group or for transcendental goals (unless they subjectively, arbitrarily happen to enjoy doing so!). Instead, libertarians tend to minimize their losses, to cut and run. In sum, libertarian group goals are continually undercut by the selfish-short-termism which is itself the prime directive of libertarianism. Hence libertarianism is unable to generate cohesion beyond the level of a leisure club - not even enough cohesion to run a political party!
This is why so many libertarians are 'pacifists' and isolationists, fantasize about emigration and other forms of personal escape, and consider suicide/ euthanasia as an obvious - first-line - solution to suffering.
He argues that this weakness of libertarians leaves us vulnerable to being taken over by theocrats who do not share our values.
As usual when I link to Charlton, I do so because he is interesting, not because I am much in agreement. I think that ideology and personality traits are more separate than he does. That is, I think that you can be a libertarian and be willing to sacrifice for others. It is just that ideologically a libertarian tries to minimize the sacrifices that can be extracted coercively by the state.
How important is group solidarity for survival? What would happen if the United States lost the sense of group solidarity that enables our government to use military force? One view is that this would bring more peace to the world. Another view is that it would actually encourage more violence in the world. I admit to leaning toward the latter view. I suspect that most people's views on this topic are much stronger than any empirical proof that they can bring to bear.