This is equivalent to boycotting companies that sell cameras, hard disk manufacturers, computer vendors, ISPs, etc, to "think about the children".
Buying a camera doesn't directly help the creation or distribution of info you consider to be immoral or unethical. Obviously you may want to use a camera maker or ISP that actively discourages such behaviour.
I'm sure you would feel extremely guilty if someone used storage facilities that you controlled to spread CP. On the other hand, I've never felt guilty about buying a camera as I've never let anyone use my camera for such purposes.
In the camera example, you have the option of not letting people use your camera your nefarious purposes, which isn't the case here. It's more akin to supporting the camera manufacturer, who, in turn, makes things that might be used by people for crime.
If I didn't know? Definitively not.
I think this was the point of the GP asking, "How do I not unwittingly get CP being stored on my device?".
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.
Lots of people have no sense of guilt whatsoever. It's not a good thing, but with an enabling community saying "it's not your fault" it's awfully easy for people to pretend there was nothing they could do.