I think the parent's (unstated) implication is that a system that can detect and block from a list of CP hashes could also be used to block any other content.

I think the parent's (unstated) implication is that a system that can detect and block from a list of CP hashes could also be used to block any other content. For example, let's say I create an eye catching flyer image detailing locations for a peaceful protest against the firing of a Mueller. Such a system could be used to block it. Right now no one opposes building it, but the capacity once created can be easily abused.