Agreed, but think about how many people only have friends who agree with them politically, it is a similar problem in that many people seek out those who agree with them and who won't ever challenge them or their beliefs.  Last fall, a good friend of mine who is a Trump supporter asked very directly who I was voting for.  He then spent the next 2 hours debating with me the merits or lack thereof of the 2 main candidates.  It was an enjoyable discussion, but many people don't enjoy being challenged.