If anything, the quality of them has gone up since most of the "I just want lulz" people went to reddit. The software is better than ever too, with Discourse and XenForo adding modern web features.
There's also a few "new reddits" like Tildes which are quite good.
No single one of the above replaces reddit as a whole, but combined I find it much more enjoyable than reddit these days.
Why do we need centralized forums anyways?
Unfortunately, all of that was a lot better 10 years ago.
That rarely happens in practice. Knowledgeable people's comments have to be made at the right time in a post's popularity window (< 24h) for it to have been upvoted early enough for other users to see. If you come across a thread that's even a couple of days old, on a popular sub, you won't bother commenting because you know no one will see it. Unlike a message board, new replies to an existing topic do not take it to the top of the thread list page.
It is usually the opposite situation that is true. A certain post hits the Reddit front page (usually a meme or political post), and all of a sudden the community is overwhelmed with new subscribers, who are either trolling/brigading because they don't like the content, or simply bringing down the quality of the conversation by posting more memes etc., because that's what they think the sub is about.
Those whose criteria include "their commitment to free speech" usually have an ax to grind about something, which would explains if they've been banned from other places before.
Not really in Metafilter's case. It's norms changed under the feet of a significant fraction of its long time community members. I also wasn't talking so much about norms than a rather narrow range of orthodox opinion.
To put it in HN terms: think of it as a forum where it's orthodox to love Ayn Rand, think in Objectivist terms, and a transgression to voice anything but the most indirect critical perspective of her or her ideas. You might not realize it because there are tons of great threads about other things, but God help you if you venture the opinion that the government should increase mandatory taxes to fund assistance programs for the poor.