I think what you're miss is the safe harbor parts of the DMCA in the USA. They offer protection for any user generated content on the web provided the operators

I think what you're miss is the safe harbor parts of the DMCA in the USA. They offer protection for any user generated content on the web provided the operators respond to DMCA requests within a certain time (24h?). Without these safe harbor provisions the idea is that the web would crumble under the weight of liability. Think about shared hosting companies, AWS, a public forum like this and then consider how much effort it would take to police the amount of content being created by users.