Old school radicalisation
If we removed the internet people would simply go back to being radicalised by what they read in the papers, in campaign pamphlets, or see on the news or in documentaries, they would go back to organising responses in person, by phone or by mail.
Of course "radicalised" has these days been redefined from being "motivated into wanting to do something about it" to "wanting to kill because of it". It's a jump from protesting, writing letters, egging politicians, to murder, but that in itself is not entirely new; it's just the most extreme direct action.
There are three parts to "the internet is to blame"; providing the evidence and propaganda which radicalises and motivates a response, providing justification that an acceptable response includes murder, allowing the response to be organised, coordinated, even financed.
The internet is not however responsible. Its only crime is that it allows people to be 'better informed'; be that rightly or wrongly informed.