This is SUCH an interesting topic, Terry! I just got a book from the library called "First Impressions". I think it's primarily written for people in business to improve their social/conversation skills, but it would certainly apply to anyone who talks to people, and desires to have friends.
You're completely right - it is so ill-mannered, and it is epidemic! I feel the same way as you do - it just amazes me. I also feel sorry for people who feel so compelled to do the things you are describing. They have no idea of the loss of friendship they experience as a result, and true friends are one of the riches of life!
Do you think the internet has exacerbated the problem somewhat? I mean, i notice especially younger people, google something, read a few web sites real quick ,and act like instant experts. In the old days, you'd have to get a library book , or buy a book, on whatever you wanted to learn more about. Thus, no one could really be an 'expert' on everything, unless they had time to read books all day. And being forced to read a whole book on something allows more time for reflection and critical thinking, and of course, covers the topic in a deeper way, hopefully. (i'm not "demonizing" the internet at all - i LOVE it myself. )
People love it when you ask them about their beliefs and opinions. They appreciate it when you try to understand where they're coming from, and acknowledge good points they make that you never thought about before.