Yes, I agree. But these people do continue to be influenced by information in the public sphere, although they do tend to select sources that they agree with. They also were influenced when settling into their original positions.

I really don't think this general behavior will change, but it's not all or nothing, it's a matter of degress. I think everyone does this at least a little bit. Unfortunately, a lot of people do it a lot. If you can shave away at it a little bit at a time, it could have a large impact in the end.