What's ominous is the growing media separation between the two political sides leading to ever-increasing difference in worldviews. How can we negotiate and compromise when viewpoints are so diametrically opposed that no middle-ground can be made?

This. It’s already bad enough with segmented Twitter follower graphs and Fox News. Just imagine when they’re entirely walled off from one another

>I don't think it's ominous. Different platforms serve different interests and demographics

Split into two separate social networks dramatically increases the echo chamber effect.

e.g. on reddit someone from /r/conservatives might still interact with /r/liberals because they both have an interest in /r/succulents

They may not be speaking about politics but they're still interacting. If you're on two different platforms even that minor overlap falls away & that allows for the two to drift further apart and harden in their views