It's also illegal to operate a meth lab in your basement, but the government would still be required to have probable cause to grant a warrant to look in your h

It's also illegal to operate a meth lab in your basement, but the government would still be required to have probable cause to grant a warrant to look in your house without your permission. You don't start with the premise that everyone is doing illegal things and must prove otherwise, which is what this system assumes. Your argument of it being a moral requirement is dubious. If you really wanted to stop CSAM why not we all live in glass apartments like in Zamyatin's We? To what extent would invading your privacy be acceptable to you if it means we could stop some or even all CSAM distribution and production? Once you decide that it's a moral imperative then you accept that any erosion of privacy in the interest of saving the children isn't off the table.