Places would change up and down in tone and attitude since the days of Usenet, BBSes, and FidoNet. It's not the platform, it's the people. How the world is in RL affects how people talk online, and the world changes over time.

The simpler answer may be that your feed has changed some since you started and you're pulling in discussions that have a different vibe than when you started. Just as you can grow your feed by browsing around, you can cull certain places that tend to be darker by blocking people or instances.