When I was a kid, I ran a public server with Logblock and anticheat but no other plugins, so it was basically vanilla for anyone who wanted to play nice. People loved it.
Public servers with e.g. coreprotect for rollbacks are still around. Most people play nice, but when somebody doesn't their acts can be reverted without impacting anybody else. It's a lot of fun if you can get the right team of admins/janitors to keep it running.
Maybe, but back in high school, it was very hard to find those. Especially with things advertised as "vanilla" or "semi-vanilla" actually having tons of crap installed.