As some got at in the comments, the dog metaphor breaks down in a few (rich) ways which Schneier gets at a bit but doesn't make explicit. I don't care about a dog seeing me naked because there is nothing about my being naked the dog can communicate in a way that I might find objectionable. If I were doing something where that was possible, I would object to the dog watching me. Computer systems are quite capable of communicating arbitrary information once they have access to that information.