You can participate in only certain subreddits, but you'll still get a lot of trolls. As far as I'm aware, this is more of an issue in trans and feminism related subreddits. This is the reason for having certain "safe spaces" like r/creepypms. Outright banning people who don't go along with the topic is far easier than policing discussions.
Brigading in reddit has always been an issue and it's likely not going away for a very long time. That's also a cause of inter-subreddit mixing that can lead to abuse.
You're mostly correct that if you stick to the smaller and more moderated communities, you'll avoid a lot of the crud.
Edit: and to be further on topic, the r/opiates subreddit also gets a lot of outsiders going in and flinging abuse at the users there.
Brigading in reddit has always been an issue and it's likely not going away for a very long time. That's also a cause of inter-subreddit mixing that can lead to abuse.
You're mostly correct that if you stick to the smaller and more moderated communities, you'll avoid a lot of the crud.
Edit: and to be further on topic, the r/opiates subreddit also gets a lot of outsiders going in and flinging abuse at the users there.