The internet and the real world don't exist in separate vacuums. Internet communication and amplification of hate speech helped create an environment where hateful sermons were planned and popularized, and vice-versa.

Facebook pages and posts espousing these viewpoints (using sensationalized or completely fictional justifications) were then amplified by the algorithm. The amplification reached people that were not otherwise inclined to participate, but were convinced through information they received online.

You can't have one without the other. Influence is driven through both in-person physical events/marketing and online platforms. Categorizing the online influence as a "sideshow" completely misinterprets how important online communities have become in radicalization. "Reach" is a key social media metric for a reason.

Reach is indeed important. But the internet is not the only way to generate reach, nor necessarily the most effective one. During the riots in 2012 and 2013, 2% of the population were using the internet https://data.worldbank.org/indicator/IT.NET.USER.ZS?location... and there were 14 mobile phone subscriptions per 100 population https://data.worldbank.org/indicator/IT.CEL.SETS.P2?location... Meanwhile, a traveling monk wanting to hold a sermon about the importance of shunning Muslims could rely on the local religious community to deliver him an audience, and on word of mouth, flyers and posters to inform everyone who didn't attend.