I suspect that people feel compelled to push their views on others in an effort to protect their sense of self. Not so long ago most people lived in small and insular communities who shared belief systems as a natural and unexamined consequence of their shared and interdependent lives. Those belief systems were essential to their personal identities, and went nearly unchallenged. Today the communities are gone, we live as individuals or nuclear families seeking social connections that were once built in and unavoidable, and the lack of those connections makes us insecure in our own identities. Any challenge to our own beliefs feels like an attack on our precarious identities and so we attack the challenger or throw up defensive walls.