Popular thought is that stepping outside of your filter bubble and seeing what people from other political backgrounds say online will make us more moderate. Bail’s and the Polarization Lab’s well designed experiments show the opposite: stepping out of your filter bubble makes you more extreme in your views. Their thesis is that stepping out of your bubble calcifies your identity, makes it more salient to you, and makes you more likely to express it. That process is largely a function of how extreme other views are online, so it holds now but may not hold forever, and a valuable direction for moderation work in social media is to dampen the visibility of extreme posts and promote moderate posts and contributors.
Unfortunately, Bail’s book takes a very pragmatic approach. He wants you to come away with things you can do, and I think the book suffers from it. I would appreciate a far more technical text diving into statistics and methodology. This is not the book for that.