You can’t explain a change with a constant. We’ve had capitalism for centuries. Far right and Islamic terrorism are not new, but they have risen greatly, and their spread is linked to extremism on the internet.

Most Islamic extremism is spread through mosques and prisons, at least in Europe. I can't remember the last time a terrorism investigation tracked the original radicalisation back to the internet. It's a non issue.

ISIS at is peak had a significant web presence.

Good point, but I'm struggling to remember people who were radicalised exclusively through ISIS websites. There probably have been a few just because there were so many cases by now they all blur together a bit, but usually ISIS sympathisers seem to have been exposed to a lot of ISIS propaganda during sermons. They may also have consumed online content but it was in addition to, not in replacement of, traditional offline radicalisation.