When reports are anonymous, you'll have trouble suing for libel. When the output of the site isn't a stated fact ("person x did y"), but a "calculated probability" without actually producing any of the reports ... good luck proving that the probability of you recklessly driving is below 50%.

It's not an easy decision, but I lean towards "should be illegal if done anonymously and without proof".

So you’re saying if I wrote a post on NextDoor saying you were a bad driver (no proof) and putting your license plate that should be illegal?

Would it be a civil thing where you could sue me for some amount, or would you make it a criminal infraction?

It's a thin line, but mostly I'd regulate the platform to not allow anonymous slander. Between individuals, it's most likely a civil issue, I'm not a huge fan of having criminal law creep into everything.

I'm pretty sure that "no anonymous slander" reduces the amount rapidly, so you end up with a bunch of legitimate accusations that people are willing to stand for because they can provide evidence. The whole "I don't like his hair, so I'm going to make up stories about him" stuff goes away.

Well yes but reality might result in no cases because the victims cannot afford the legal fees, for example. It's a complex thing.