Yeah, I would say that algorithmic curation is the key difference between "before" and "after" here. Social media makes it easy to form filter bubbles, but on its own it's just an iterative change to an existing phenomenon. But when you curate and present content for engagement, especially content from outside of your chosen set of interactions, it becomes a positive feedback loop of ever-increasing extremism - even in the most benign of topics.

Google's search personalisation and targeted ads fall under this even if they're not as effective at radicalisation IMO.