You'd be surprised. Lots of offenders are very low sophistication. If you read news articles about how a particular offender was caught with illegal material, so so often it's because they uploaded it to a cloud provider. It's not a one-sided tradeoff here.
What percentage of offenders victimize children and never record it in any way? If that's the overwhelming majority of abuse cases, what are we even doing here?
Worse. Only a tiny fraction of child abuse material cases actually get investigated due to lack of resources… this debate about scanning is an insane distraction.
