The point is not that we're using tech to prevent something. The internet does not prevent pr0n, after all. But that you can't treat a human problem as if it was a tech problem merely because the tech allows it to happen easier.
My point was that the underlying problem is that some people want to look at porn instead of work. That's the problem we have to solve. The internet is just a symptom, it allows those people to pretend to be working while actually looking at porn. The solution is not to cripple everyone's internet access. The solution is to either change the people, or change those people's attitudes, so they don't want to watch porn at work. It's a human problem so it can only be solved in human ways.
With CSAM, the problem is not that there's child porn on the internet. The problem is that some people like to abuse children. We need to solve that problem. Monitoring every byte sent over the internet is not going to solve that problem. It's a human problem. We need to work out ways of detecting these people sooner in life and either help them over it, or remove their access to children. I'm not a social worker so I don't know how we'd solve that problem.