In 1858, when London could no longer tolerate the stench of raw effluent in the Thames, city authorities commissioned a system of sewers that operates to this day. A century later, when noxious fog choked the capital, parliament passed the first Clean Air Act, limiting coal fire emissions.
When a dangerous toxin assails the senses, polluting public space to the detriment of all that use it, the case for legislation is self-evident. The argument is more complex when the poison has no chemical properties; when it exists in a virtual realm. This is the conceptual challenge for regulation of digital content. It is made all the more complex by conflation with arguments about free speech and censorship.