One of the major factors that keeps it relatively clean is that user registration costs $10. That's a strong financial disincentive against trolling, bots, etc.
I really believe that successful online communities of the future will have paid signups.
I'd totally pay $10 for a less shitty reddit clone.
When I use Facebook I am the product, not the customer. This means the platform is optimized to put my eyeballs on advertisements or provide data about me to marketers. It is not optimized to provide high quality conversation.
No wonder you got banned so quickly there...
Having a toxic community that internally declines to moderate is not strong moderation.
1) Namespace of subreddits. The subreddit which snags the most obvious name for a topic has a much better chance of becoming canonical for that topic that competitors with worse names.
2) Cross-subreddit identity and supporting tooling. For example, i can easily search for all recent posts made by a particular user, but i can't easily search for all posts made by a particular user within one specific subreddit. This sort of thing promotes "cultural leakage" across reddits and makes people think of all of Reddit as one community with one culture.
Related: see https://news.ycombinator.com/item?id=16573842 which summarizes a study that finds cultural leakage across subreddits.
Forum communities with actual strong moderation, eg. Something Awful, ResetEra have near zero issues with hate speech, Nazis and other things that reddit has let fester.