The real crime is child abuse. Material related to that is also illegal because it presumably creates demand for the abuse. Whether that's actually true I don't know.
> if you polled the US that any sizable portion
No, but they also would agree to that they should have an option to keep their data privately. Maybe the public should be polled about this tradeoff?
For example the case of virtual CP has an interesting legal history https://www.freedomforuminstitute.org/first-amendment-center...
It is fine if this is your argument, but you don't have to wrap this argument in with the very legality of CP. You can acknowledge something is and should be a crime while also being against these type of automated dragnets to find people guilty of said crime.
But there is a clear tradeoff between the two so saying that would be a useless platitude. If we really see the internet as an extension of our vocal chords, then we should have individual rights to it, especially considering the fact that the internet infrastructure is not provided by the governments themselves, only the spying is.
Actually it's legislators and the courts that come up with these laws and they are complicated. The question is if these laws reduce child abuse or simply increase spying, and in the end what is the acceptable balance between these two.