While laws do vary from state to state, in most areas there are exceptions. For example, if you have a Restraining Order against someone, then you can record any and all violations of that order without notifing the caller (check your local laws). Victims of domestic violence use these recordings to prove harassment and threats.
Disabling the recorder because it might be used unlawfully is just sad. The GPS, the camera, and the phone itself could all be used in illegal ways.
I would just like to have recording capabilities to be able to take "notes" at times when I can't write it down. Having the app announce that recording has started/stopped covers the legality.