It depends. One forum where I spend some of my time has very hands-off moderation and it does have a) some quality conversations b) diversity of opinions. Of course it descends regularly in low-quality drivel, insults and/or shitposting, especially on controversial subjects, but it works.
Edit: But I can't say that it works everywehre, just that it can work.
It's the case on that forum and the off-topic discussions (religion & politics) are accesible only to accounts older than 1 year, so it helps to limit shitposting in those discussions. Accountability for your opinions in that case just mean getting mocked by other people (I said free speech, not nice speech).
I just wanted to show an counter-example disagreeing with your (apparently) absolute position.
Yup! That's one of the good ways of holding people accountable.
Of course the limited reach of the spoken word and inertia of the speaker put limits on how much shitposting you can do in meatspace, but sometimes it's still preferable to have as little moderation as possible and instead enable each user to filter outer the noise on their own.
If there is one thing I wish I could beat into people's heads with a stick about online discourse, is that any place free of moderation is not going to be a free speech haven, but a cesspit where the people with the most free time will dominate and drive out others.
It's incredibly cheap and easy to shit up a conversation, but quite costly to have an engaging dialogue. By having no moderation, you're actively choosing to reward shitposters, and punish quality contributors.
And, no, adding an up/downvote mechanism does not solve this problem.