I think this is painting a rather stereotyped view of people on the left. I share most of the views of the left, however don't end relationships with people over it, preach, or attend any seminars. I think you're seeing the vocal minority here, which is of course more outspoken as they care enough to talk about it. Apart from the most extreme people, I have had many productive conversations with people whose views were more left than mine and haven't been ostracised once.