In my experience, this has always been a problem after a forum grows beyond a certain size. It’s not really a Reddit-exclusive thing. It’s also not related to karma/reputation-tracking, IMO.

Early adopters of a small, somewhat empty community are people who want to grow the community and encourage posting. Discussion is bright and careful in certain ways because it’s usually just a few commenters interacting with each other who all want the same thing.

Once a community grows big enough to support lurkers and a variety of topics, with multifaceted discussion happening naturally, you have a familiar effect happen: you know how people are disproportionately more likely to review a product or business if they had a negative experience than a positive one? Well, in a similar way, when there’s enough content to lurk (and not be one of the early enthusiasts who post in spite of a lack of content, as a duty to help the community grow), then lurkers are more likely to come out of the woodwork and join a discussion when they see something they disagree with or feel strongly about.

Honestly, though, it has a few silver linings. I grew up learning a lot from arguments online in various places. Sometimes they are handled well and sometimes they are handled poorly by the participants. Learn from both. It’s great to see two sides of an issue, even a petty one. It can teach you a ton about how to behave well, how to actually persuade someone on a topic, and how to avoid conflict in the first place. It can also teach you about a controversial topic you knew little about, and spark your curiosity to learn more (if only to refute something with citations) and sometimes change your opinion altogether.

The healthy/toxic dichotomy starts in your own mind. You can’t control others, but you can control yourself. So find those little positive nuggets where you can.