Good analogy. If there was a tool that could do everything a knife can do without being able to cut people, knives wouldn't be nearly as common and anyone who insisted on carrying one in public would be suspect. "I need it to cut vegetables," would not be a reasonable excuse, because there's an alternative.

There is an alternative to your stealthy camera glasses, which you are aware of, and your admitted use case for them is filming people who are unaware that you are filming. Yet you can't imagine other people use them for the same purpose? I'm trying to assume good faith but you're not making it easy.