Does not matter if someone else put it there without your knowledge. Or maybe it matters, but then it's on you (for all intents and purposes) to prove that it was without your knowledges.
The purpose of strict liability in possession is to prevent the defense that someone does not know the legal status of an item in their possession. It does NOT prevent the defense that someone does not _know_ something to be in their possession.
For example, it is not a defense to have drugs and claim "but I didn't know they were illegal". It is a defense to claim "I did not know they were there."
In drug cases with actual possession, it is difficult to support a defense of "I didn't know they were there", which is why charges typically result in criminal liability. They drugs were physically on you, and unless you have evidence that someone planted them, it is unlikely you could establish reasonable doubt.
But in cases of electronic material for networked devices, there is most certainly an affirmative defense to counter actual possession and constructive possession. Computer devices are hacked all the time, and network & device logs exist. For example, if a prosecutor agrees to the fact that a defendant had no knowledge of the material, a judge would toss the case and a jury would not convict you. The law is not meant to pedantically convict you of non-crimes.
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.
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.
This is a wild and in my opinion a wrongheaded analogy. Possessing CP is a crime by itself. It doesn't matter if the person possessing is actually a molester or not. It is just like the possession of drugs being illegal and it does not matter whether the person has actually taken or plans to take those drugs.