Have you ever thought why and who demands that? In my experience, it's the rightwingers. As usual, we're supposed to sit down and shut up while they impose their ignorance on us and the world. I've been in many groups with non-consevatives and shared a sweeping and uncontentious exchange of ideas and perspectives. For example, progressive people of multiple faiths, or no spiritual faith; and everyone showed genuine interest in each other's faith experiences.