But that's not my point, 4chan has clear rules that are not about illegal content: https://4chan.org/rules. There are moderators/janitors enforcing thoses rules and a report system. The first rule is:

"1. You will not upload, post, discuss, request, or link to anything that violates local or United States law."

But that's only the first rule. There are 17 global rules, and each board has a few.