You wrote: "He is in a prison of his own choosing," and this points to a fundamental problem with the very label "incel." The "in-" part is a contraction of "Involuntary" - an attempt to claim "this is not my responsibility in any way," and place all responsibility for lack of human connection and intimacy on others, individually or collectively. But when someone takes no action on their own behalf, how "involuntary" is their state of being?

That said, he is not fully at choice. Our society breeds this - most of our institutions care little or nothing for people as human beings, seeking only to maximize extraction of material wealth, directly or indirectly. We do not intentionally or broadly teach (or practice, which is a manner of teaching) compassion, mindfulness, human relational skills, or any such basics of being healthy humans. We even discourage or denigrate those practices in far too many contexts.