Libertarianism is based on rights to life liberty and property
In order to maintain those rights requires cooperation, or should I
say collusion, on the part of a group of people to supress other
people who might 'deprive them of what they believe is rightfully
theirs. Feudalism... A form of government. As an anarchist I only
would support that sort of cooperation or collusion for existential
self-defense. ie. to defend against Fascists who, by ideology,
believe because 'A', 'B' has no right to exist.
As far as property... If someone tried to steal my computer I'd kick
the living shit out of them, but I wouldn't be 'calling a posse' to
help recover it if they got away with it. I'd 'deal with it' myself.
And fwiw "Liberty" in the US constitutional sense of the word means
'the liberty to own property' including people.