It seems to me that selfishness/self-interests is a biologically inbuilt part of human nature. Fundamentally, we all want more; we all feel that our lives would be better "if only" we could have more of something or other.
For me, libertarianism is mostly an intellectual rationale to help justify and support our continual desire for "more."
Every ongoing personal relationship requires that the individuals must constantly struggle with resolving their own individual interest when it is in conflict with the interests of the other... or the relationship.
And, to a larger degree, I feel that there is an inevitable tension in the social contract where every individual will feel that he/she should have more... and that he/she has less because of what is (inappropriately) going to other(s).
And, IMO, libertarianism provides the perfectly honed intellectual rationale to explain why I should have more as a sanctified natural right... as opposed to mere personal greed.
As far as I can tell, in any arrangement of society, there will always be people who feel they have been deprived and are entitled to "more." I think that cannot exist a society where libertarians would not make their arguments to support a reduction in "social oppression" in favor a fuller expression of "natural rights".
The argument of libertarianism seems to imply that there exists some idealized social structure that would (almost scientifically) resolve all tension and conflict by correctly attributing all rights and goods according to natural law. IMO, this would be less possible than having a human couple with no augments or disputes between them.
"It's not a lie if you believe it." -- George Costanza The whole problem with the world is that fools and fanatics are always so certain of themselves. --Bertrand Russel