So honestly it's best use case is "gotcha". As in you didn't know I was recording and you said something stupid and now I have a recording. Likewise if you are talking to someone and you say something along the lines of "Are you sure about that?" or "Can you confirm this is what/how you want me to do this" and then you record the audio for later incase they come back and say "I never said that".
For myself I went the extra mile to just have my laptop record ALL audio but then felt this was a little too douchey/NSA-y and disabled the whole thing and wiped the audio. I wanted such a system not only for "You said this then and now you are saying that now" but to remember things I had said myself. I wanted to hook it up to STT to have a searchable archive of what I had said but again it was an invasion of privacy (to people around me) that I personally couldn't stomach.
As for creepiness, you know what's creepy? People saying something and then lying about it later.
You'll be happy having the audio even if there are restrictions. Simply don't tell anyone about it until the benefits (saving your ass) outweigh the drawbacks (potential charges).
To circumvent the one-party consent issue, he could just write a Terms of Service on the inside of his shirt that includes a clause about "Engaging in conversation as a use of the Services" that implies agreement with the Terms of Service.
Virtue signaling. By implying that you're a criminal they feel it makes them look better.
As for you, there's nothing morally wrong in wanting to not be trapped by a liar. And it doesn't magically become morally wrong if you walk into a two-party state.
For myself I went the extra mile to just have my laptop record ALL audio but then felt this was a little too douchey/NSA-y and disabled the whole thing and wiped the audio. I wanted such a system not only for "You said this then and now you are saying that now" but to remember things I had said myself. I wanted to hook it up to STT to have a searchable archive of what I had said but again it was an invasion of privacy (to people around me) that I personally couldn't stomach.