As an outsider I think other core problems of the US are corporate capture of the legislative process and gerrymandering pushing candidates to extreme positions.
Extreme positions are just the reality of 2019 culture. I was reading a Twitter war about whether or not a professional Hearthstone player was paying enough attention to the game during one of his matches. It was a sea of hate-filled vitriol from both sides. Reading it, I was honestly a little sick to my stomach seeing what social media has become.
If we're going to get that upset over a children's card game, it follows that we're going to get upset over things that actually matter.
For example if you are running for a congressional seat which is 50% republican voters and 50% democrats I would imagine that being a moderate centrist is probably a relatively good strategy.
If the seat is 80% one side then probably you want to be much more extreme in that direction because what the other 20% thinks doesn't matter so much.
However I agree, the internet was meant to make us all open minded and tolerant and yet has had the opposite impact.
If we're going to get that upset over a children's card game, it follows that we're going to get upset over things that actually matter.