Something should be both extreme ideologically, and a relatively small minority to be "fringe".
Mostly, interestingly enough, the premise of these contrasting groups and opinions are actually based on the idea that some third party external group is imposing on their freedoms and well-beings. Romans laid continents under their taxing rule by fear mongering, nothing new and you hardly need a free and open digital global communication network for that.
My personal belief here is that these developments will self adjust. Unfortunately through great friction and pain. Any open society that eventually submerges into the rule of a "Trump/Bannon" group, will eventually self destruct slowly. If the core premise of a society is fear mongering of a third party external group (Jews, Muslims, Republicans, West-, East-, Capitalist-, Communist.. ) the core problem is that you're trying to fix your head ache by shooting yourself in the foot. And then the next foot from that..
Power is profoundly addictive and corrupting. If you've been a failure up to now, and suddenly you're in power for blaming some low influence group, that blame will only grow stronger and stronger with the failures of making a positive impact for the desperate people that put you in power.
I would argue that a small taste of power corrupted the left.
When they started censoring conservative views, banning conservative speakers on campuses, "no platforming", they were not defending freedom.
The comment I responded to, however, was partisan and I was simply adding balance.
* Subscribe to The Economist and read it weekly. It's designed for busy people but has real, sophisticated information and exceptional breath of coverage. It's a bit right of center, but not ideological (except their obsession with the free market solving every problem), and very credible.
* Read this news summary daily. It's a bit left-of-center, but again non-ideological and the coverage is exceptional.
https://www.justsecurity.org/category/news/
* Check the headlines at the NY Times. They are criticized by all sides for being biased against them, an excellent sign of good journalism. Their editorials are left-of-center, but ignore them and read the news:
In about 20 min a day, you'll be better informed than almost everyone you know. Final tip: Skip all editorials, columns, talk radio - 99% is either uninformed, intended to twist things and manipulate you, or both.