I just figured out the difference between those who proselytize -- religion or anything else -- and those who don't.
The ability and courage to walk alone.
Proselytizers fear being alone. They cannot be comfortable with just themselves for company. They fear silence. Solitude makes them unstable. They actively need the emotional support of someone else with whom they share ideals on a visceral level: think-mates.
This is an idea in development. More to come later.