You're assuming good-faith on the part of the police. Then using an emotional counter argument. Think about that. A police officer really believes that you're a terrible person and guilty of some terrible crime; and use that to justify a tiny little lie by pretending s/he didn't know that they couldn't do X.

Of course sane people do not want guilty people to go free. What's wanted here, and what's important here, is not that the guilty go free, but that the innocent aren't subject to harassment, embarrassment, and all sorts of other -ments from the government. And before you ask, yes, it's okay with me if some murders go unsolved due to the absence of pervasive surveillance, or even the overly liberal application of the "good-faith" exception.