@Goosefoot
It's a perfect embodiment of a type of approach that has become more and more common. On many questions even if you broadly agree but point out some type of nuance, or try to see what the best arguments of the other viewpoint are and see what's behind them, people won't engage.
I find it very odd. I didn't go to great schools by any means, but we had debating, and model Parliament, and class discussions, where that sort of thing was encouraged. I've talked to parents now who complain when their kids are asked to defend a POV they object to in a school exercise.
I'm not sure what has happened but I would really like to know.
TWITTER!!! 
People laugh or look confused when I rant say this but I honestly believe it's the main culprit why we're seeing this type of decline. It marks the spike in divisive and defensive behaviour, especially in politics, and it completely defines the echo chamber mentality, perhaps even created it, in my opinion. Don't like what people are saying? Block. Don't agree with a different opinion to yours? Block. Was someone 'nasty' to you? Block. But meanwhile, do you agree with me? Then follow, and get followed back. It has given people (mainly young people, but plenty of stupid older ones too) a disproportionate skewered look at the world around them. Then the media complicity is also to blame and it is quite worrying, framing things like "public is outraged/offended/shocked by xxxx" and then using four or five tweets from people as 'proof' causing a frenzy of comments from both sides under articles, further entrenching 'them or us': If you're not with Labour, you must be Tory. If you don't believe TWAW, then you must be transphobic etc. I've lost count of the amount of comments on here along the lines of "I went to look at the tweet you linked to but they've blocked me on Twitter but I've never even spoken to them or looked at their Twitter before". It's dangerous. Blocking people you've never met or spoken to on the basis that they might agree with things you don't agree with?
I'm sure Black Mirror did an episode on this and in the end people ended up being blocked and unable to see a single other person because they didn't share the same viewpoint. (I'm aware BM is not the greatest platform to base an argument upon...or, perhaps it's the greatest one?) I've been accused of hyperbole and hysteria and maybe it is, but it's not looking far off from what I think, imo.
and, BREATHE! (and sleep) 