Congrats, that's exactly how I started my road to "extremism", as you characterize it. Where do you think SJW's come from, exactly? You think the source is Tumblr and other internet circlejerking echo chambers? They are merely a symptom, one that is becoming more and more visible thanks to increasingly widespread worldwide communication. My extreme loathing for these people and their sacharine idiocy didn't come from some sort of nationalist indoctrination, quite the contrary. It came from constant exposure to them and their source in academia, the source of the disease that is killing western civilization, the suicidaly self-loathing crypto-marxists who poisoned western liberal thought beyond redemption. If you had any self-awareness you would realize SJW thoughts are just the logical end result of the "progressive", anti-nationalist, pro-globalization, so-called "humanist" ideology you still adhere to. You're no better than the "moderate" islamists making excuses and pretending the deeply imbedded pillars of your ideology are completely blameless for these embarassements, as if there were absolutely no connecting thread between them.
Right, but reacting with anger towards them only makes them feel more confident in their issue ("If they are so mad that I'm bringing |patriarchy/homophobia/transgender issues/other unrelated shit that I blew out of proportion| up all the time, I'm basically the 21st century Rosa Parks!"), generally yelling on the internet is a bad way of getting your point across.
And you are right, the internet almost completely removed the need to adapt to our society when we're somewhat not fitting in with our point of view, instead it helps people form small circlejerks left and right, where instead of discussion, everyone just says what they think and expects to hear it back from others. It's natural that we flock to people sharing our POV, but there arises this problem of "proudful ignorance", when instead of even considering the opposing idea for a moment, it's quickly dismissed as something wrong and stupid because "my idea is different"
And then again, our experiences vary because different countries have different "leading" ideas, I for one know that Polish internet is absurdly right-wing, or more often simply reactionary - "what is now is badder, we want to go back to the previous thing even if we hated it" kind of thinking. Common for all of us is reddit, tumblr, 4chan and facebook I guess, and I'll refer to them.
It varies and I'm probably horribly generalising, but GENERALLY: Reddit appeals to young males (varies from sub to sub), tumblr is more appealing to younger women and teenagers, 4chan is generally same as reddit, but with more hating and shitposting and facebook is for old people. All those places create different views of the world based on how their users post and "discuss" (if you can call it that), and what the general consensus eventually becomes. And even in those sites, there are very varying opinions.
Also, universities are definitely to be blamed but I can't really speak about it as all I've ever heard is some failed attempts by student councils to create some stupid "safe spaces" in a few colleges in the US, and a few protests + the BlackLiesMatter movement which is a fucking joke. But can you blame the universities? It's their job to spearhead the new ideas, sometimes it fails and sometimes it goes through, sometimes for worse and sometimes for the good. Someone oughta do it, the problem is when you can't speak out AGAINST an idea.