OK, interesting. I guess it's a personal thing. For me it's not just a question of whether I know or not. I also have to consider if there is anything I could reasonably do to prevent such things from happening. If there isn't, then I would consider whether I really need to use the system (for example, is this my only option because I live under an oppressive regime?).
I think this was the point of the GP asking, "How do I not unwittingly get CP being stored on my device?".
So you wouldn't work on a company like Dropbox or any other of those file storage systems? Or a VPS/cloud provider? Or an image hoster?
And what about physical things? If you're working on a retail job, the customer buying piece of rope may be planning on using it for tying people up. The guy renting a car may be planning to use it on a hit.
Ultimately, it's not possible to keep track of everything people do with the services we offer.
If I didn't know? Definitively not.