And it is your approach is naive. You ignore technology. You can not technically limit information propagation in any kind of network. It will find a way. But if people will think that the only reason to go to any time of crypted network - is to fetch CP - here we go - society prepared for laws preventing cryptography (you can be imprisoned in UK for not giving crypto keys for a several years!)
Again - we might want to work on technology recognizing nudity, or abuse or whatever and protect ourselves and our kids or our moms from this type of content, but this should be completely separated from technology used to share this data! Just like there are parts of big cities which are not safe for white/black/chinese/etc guys. It doesn't mean we have to put tall wall around this part of city. Instead whoever think it is not safe there - just do not go there.