The bad actors were much less prevalent back in the heyday of small phpBB style forums. I have run a forum of this type for 20 years now, since 2002. Around 2011 was when link spam got bad enough that I had to start writing my own bolt-on spam classifier and moderation tools instead of manually deleting spammer accounts. Captchas didn't help because most of the spam was posted by actual humans, not autonomous bots.

In the past 2 years fighting spam became too exhausting and I gave up on allowing new signups through software entirely. Now you have to email me explaining why you want an account and I'll manually create one for the approved requests. The world's internet users are now more numerous and less homogeneous than they were back when small forums dominated, and the worst 0.01% will ruin your site for the other 99.99% unless you invest a lot of effort into prevention.

phpBB forums have always been notorious for capricious bans based on the whims of mods and admins, it's just that getting banned from a website wasn't newsworthy 10 years ago.

As a moderator of one of such forums, all of the behavioural issues have been a staple there too. We always had to moderate not just spam, racism and insults, but also "that dude that rants about his pet peeve in every topic", "that dude that rants over Apple even in topics where someone is asking how to change keyboard layout in macos", "that dude that's obviously mentally ill" and many others.

It was always a job of ensuring a comfortable environment for the community gathering on the forum and it did require "censorship" beyond obvious to prevent a minority of users from souring the environment for everyone.

The problems didn't exist as much because people didn't usually come across communities they hated/disagreed with unless they were searching them out, and every community could set the standards it wanted to set. And I think that's where large social media sites can't work; they put a bunch of groups, many of which deeply disagree and dislike each other, on the same site/platform and have to try and keep the peace without said groups getting into flame wars and personal attacks 24/7.

Small, indepedently run communities could set their own standards, and those that who disagreed with any one set of rules could go and find somewhere more to their liking. Reddit and Discord have this to an extent, but even then, it's too centralised and too heavily controlled by one organisation.

Hopefully if Mastodon takes off, federated services will bring this style of community back, except with the ability to take part in other communities if people agree with that.

That's because they were small and often has strict rules (written or not), aka moderation, about how to behave. You don't remember massive problems because the bad actors were kicked off. It falls apart at scale and when everyone can't/won't agree on "good behavior" or "the rules" is/are.