Karma sucked ass on Reddit. Essentially people could ban you from participating because you pissed too many people off even though you didn't break any rules.
Karma count is an ass kissing metric, high karma shows that you kiss people's asses for upvotes, low or negative karma shows that people dislike what you say which is absolutely ok. People having different opinions vs going with the group is the difference between a healthy platform and an echo chamber.
By the way Trolls and malicious actors who that system is targeting should be dealt with directly. If someone's posting hateful transphobia instead of downvoting their acount they should just be BANNED from the community or the platform as a whole, keep bad people out of the community.
So you don't think people who post hateful stuff about trans people or deliberately spread dangerous or hateful misinformation, or people who spam multiple comments at once should be banned from the platform (or at the very least have their comments actioned by mods)? I'm saying that because Reddit originally intended the Downvotes system to be used to combat those specific types of scenarios, they said it was to control spam and malicious actors. These are things that should be dealt with using disciplinary action i.e. being booted.
If it was an agree/disagree system like many people think it is they wouldn't have added rate limiting to people with low or negative Karma or made it so communities can set karma restrictions.
Even so I don't really think it's a good method either, it's almost just a softer less obvious form of shadowban.