So we must shut down all hotels because they all unknowingly hosted some illegal activities in their rooms, e.g. if someone met a prostitute there?
In fact we cannot have people rent out condos or houses anymore either because illegal stuff will happen there and the owner is responsible even if they don't know!
Also we need to shut down all ISPs because at some point in time illegal data was cached on their machines during transit!?
I don't think this deserves downvoting, because it gives an opportunity to point out 2 things I didn't.
1) The crime in question is not just that you acquired the content, but that you disseminated it. This is in sharp distinction from a hotel, in which the person renting the room is the perpetrator. It's not like there is some RICO statute that hotel owners routinely get pinned with when renting rooms out to shady people unless they are literally involved in RICO.
2) CASM is unique among crimes (in the USA) in that knowing of it and NOT reporting it is itself a crime. You cannot claim that you were frightened. So you now have to prove that you never decrypted it yourself, on top of evidence that you disseminated it.
That's just the reality of the world today. Anything regarding crimes on the Internet, it's almost always the defendant being guilty until proven innocent, especially against cops/DAs with a dearth of technical knowledge.
You may be innocent, but you'll be spending tens of thousands of dollars and a chunk of your life agonizing over it before "justice" is realized.
You do NOT want your defense in court to rest on convincing a judge or jury of this.