Sending the email and messages is what the user does.
Auto-sending all your photos to a server owned by someone else (and without end-to-end encryption!) by default cannot be described as "what happens on your iPhone stays on your iPhone" in my opinion.
It has been a while since I have setup an iDevice from scratch. Isn't there a prompt during setup that asks the user whether to enable this iCloud backup? I believe you can even setup devices without entering an Apple ID at all. Wouldn't that make this scanning also a response to something the user does?
I don't know the answer, but regardless, any non-technical user will simply not understand the implications of using "the cloud". They don't know that there is no cloud, just other people's computers and that Apple has access to all photos. I really doubt it's explained well during the setup.
Auto-sending all your photos to a server owned by someone else (and without end-to-end encryption!) by default cannot be described as "what happens on your iPhone stays on your iPhone" in my opinion.