[dvdhnt]

As others have said, this is not causation nor has hard evidence been provided, however, I am curious:

What moral obligation does a developer have, if any, to expose this sort of "feature"?

The mob came when Snowden et all exposed the large passive-collection programs run by the federal government - do people not believe that we have the same protections from private companies as we do from public entities? Yes, it's their app and I don't have to download it, but we're talking about covert activities - aka spying - that a user has not consented to.

You wouldn't let General Electric put a "passive" video camera in your oven to capture what goes on in your kitchen for the sake of a "better cooking experience" or "personalization"; our digital real estate should be no different.