In the sense of politics shifting towards the extremes and people having less productive discussion but getting more polemical.

What could be a productive discussion in today's political situation? There is no 'common good' answer to conservative vs liberal choice. It depends - good for who? Conservative is good for passive majority (remember Luddites - you could laugh at them now, but they never recovered to pre-mechanisation living standards. it took 4 generations to do so, until post-WWI times). Liberal is good for active minority. There can't be agreement - it is either us, or them win. That's a polarization, and Twitter can't make it better, or much worse.