Earlier quoted context omitted.
You can target Facebook ads with surgical precision to manipulate people exactly the way you want. This is exactly what Cambridge Analytica did. You cannot target people with such precision in traditional advertising. I don’t think it’s unfair to say social media advertising and data collection is the biggest risk to democracy that we have ever faced.
The targeted precision really is what's different. Your candidate can be N different single-issue candidates in a way that's just not possible without precise targeting. The "echo chambers" explanation, in particular, seems wrong. Echo chambers always existed.
The echo chambers haven't gotten worse at all. They've become easier to observe in action and quantify, because social media is leaving a giant digital trail that everyone can observe (whereas previously the average person didn't leave much of a partisan trail/record for observation or study or reporting). The perception that the echo chambers have gotten worse is merely the horror of seeing the already existing echo chambers in action so vividly now that everything is recorded and everyone has a bullhorn.