Since most redditors fail at voting and use the buttons as "I agree" or "I disagree" buttons, it becomes pretty easy to have a normal mainstream opinion and get absolutely crucified because you accidently wandered into yet another echo chamber. Let's say hypothetically that you were a new reddit user and not a user for over 10 years, and you walk in and say a normie opinion, and then get downvoted into oblivion by an echo chamber. What does that look like to the victim of the downvote brigade?

Originally downvotes didn't matter, they were just imaginary internet points. With automod minimum karma limits, for a brand new user, now not only did your post get piledriven into the dirt for what would normally be an uncontroversial opinion, but now your ability to interact elsewhere on reddit has been compromised.

After that, lots of people who might otherwise be good users will just say "forget that" and leave, further enforcing the echo chamber.