That is a common novice take on the problem, but it only makes sense if the only way harm happens in the world is by people accidentally seeing things they didn't want to see and that can be easily filtered out.
I think we just don't agree on what the problem is. I don't want a discussion platform protecting me from "dangerous" content that I am choosing to engage with.
Yes, I think most people feel the same way as you. The question then is what to do about the societal harms enabled by the platform.
I think that's a question for society, but also for the people working at the platform. For example, if you read interviews with 4chan founder Christopher "Moot" Poole, you'll see that he started out with a similar ethos to yours. He ended up reining in things some over time, still grew miserable with what he created, and eventually quit.
The problem is much larger for a platform that aims to be larger and not generally despised. If you look through the big platform rules, it's worth thinking about each item from a perspective of, "Am I happy devoting my life to enabling that?" E.g., the people who are into CSAM don't want protection from content their are choosing to engage with, just like you. But how many people want to go to work each day and say, "Yay, another day of supporting machinery to distribute child porn across the globe?"
A business needs to have the freedom to kick out shitheads so as to protect itself from becoming a place that non-shitheads don't want to do business with.
A grocery store doesn't let people walk around in their store saying just anything to their customers. They're (rightfully) not bound by as high of a standard for what they allow to be said in their store as the government's standard for how much they'll let you say before they imprison you.
You could say the same thing about a telephone company or a postal service. After all, they are just like a grocery store, so no need for them to uphold free speech.