I had always thought the term "spank bank" was metaphorical--a *mental* database of images and/or people one found arousing, not a literal stash of downloaded porn and/or nonpornographic images from the internet used for masturbatory purposes.

Urban Dictionary seems to agree.

Of course, in the real world, much porn is problematic, and I see why some women have a problem with it for one reason or another, but that's a whole other discussion unto itself.