Her protagonist, if I recall correctly, struggles precisely with the demands of his selfishness as an aspect of his freedom, within the context of a (revolutionary) anarcho-syndicalist society—which looks something like socialism, and something like a rejection of all isms.  He winds up in conflict with his society; I’m sorry that I don’t remember how it ends.  Anyway, you probably know it already.  I am not entirely sure that it’s really addressing the problem you’re outlining, but it’s probably worth a look, or a re-look.

There are a number of entries by Elouise that broach the topic of the introvert as psychological type (able to perform socially but requiring considerable downtime away from people). http://weez.oyzon.com

Weez does a fine job presenting the question from a first person point of view.

Back to the manifesto… I would hesitate to substiture the introvert for loner since the term “introvert” points to Jungian constructions and dichotomies that in my estimation flatten the complex dimensions of the realties to which they are applied. However the term “introvert” takes on a less either/or colouring in the Myers-Briggs Type Indicator (MBTI)where it is joined by more pairings to create a table of sixteen types.

Wikipedia provides an interesting snippet of info in relation to the MBTI:  Katharine Briggs’ daughter, Isabel Briggs Myers, wrote a prize-winning mystery novel Murder Yet to Come in 1929, using typological ideas.

A novel! That reminds me that on the politico-philosophical front some of the best thinking about the individual in relation to a group is the SF of Octavia Butler. She poses the problem especially with the telepaths in terms of an individual with contemporaneous groups of stranges or relatives as well as the individual’s relation conscious and otherwise to preceeding or succeeding generations. Space for the individual to grow and become is very much determined by a social distribution of resources—very political considerations.