Private keys don’t prove you don’t have a gun to your head.

Entering a trap phrase elicits a success response for the attacker's benefit, and then surreptitiously gives coordinates to law enforcement, emergency contacts, Mark Zuckerberg, whoever.

See, we've almost got this built!

What’s stopping someone from entering a trap phrase to... entrap the other party?

The cops showing up to a non-rape would probably be the kicker.

Not that I think this tech should exist or be necessary in the first place.

or that you aren't drunk, had your phone weakly secured and accessed by someone else (passed out and they used your fingerprint or something), or probably a number of other possibilities

Huh. That almost sounds like requiring someone to take some personal responsibility for their own security!

Something we as a society, especially when it comes to tech, need to strive for much more.