When something bad happens (like, say, a murder), people want to talk about it. But now, the conversations happen in view of the public--the _whole_ public. So people don't want to be on the wrong side of the conversation. In private, among friends they understand and trust, they might express doubt or complex thoughts. But out in the general public, where their opinion could be boiled down to a soundbite, they don't dare lean on nuance. So, they play it safe.
Go onto Reddit, and under some controversial story post a nuanced take. Chances are you'll get downvoted to oblivion. And that's fine--it's pseudonymous. But if it were attached to your real name, and you happened to be wrong (or some part of your statement could be taken out of context and made to look wrong), then it could always be dredged up and used against you. OTOH, there's basically no scenario where it would be dredged up to help you.
So the result is, all nuance is drained out of the conversation. We end up with junk food for public discourse: no fiber, no nutrition, just feel-good sugar: "fuck that guy, he should be locked up for life!" And seeing everybody carry that line unanimously makes anybody who doesn't look immediately suspicious.