You're right! That hypothetical and highly unlikely scenario is completely worth all of the ways in which the tech could be and is being abused.

If it's so hypothetical and highly unlikely, then we've nothing to concern ourselves with over the fact that Google will comply with attempts to rescue these hypothetical and highly unlikely endangered people. After all, if it basically never happens, Google will basically never grant the extrajudicial request.

Would it be so difficult for Google to add a configuration step where people can explicitly consent to this?

The short answer is "yes," but I would be in favor of it being added. Of course, it's not going to secure your data if somebody that isn't you is the one under threat of imminent harm or death and Google believes the data you are holding could save their life.

If that data is so relevant, then why can't they get a warrant?

Urgency. In the event of kidnapping, chances of successful rescue vs identifying a John Doe body six months later can be measured in hours.

That's fine, as long as we're clear that is said in a position of privilege.