This doesn't make sense, since it's advertisers who are the ones putting pressure on sites like Twitter to stop spreading extremist content.
The problem is that humans are extremely willing to enter echo chambers where they are told they are right all the time. That's what they will do by default. So if you optimize for engagement, they will radicalize themselves very quickly. If you figure out how to power a social network without ads, you will get something a hundred times worse than Facebook, because there will be no pressure to moderate content at all.