The GoPro is normally used in situation where some preparation was already done (e.g. register for some activity, prepared your gear, trained for the occasion) and the "best camera is the one you have with you" adage doesn't fit as much.
Putting you mobile phone in some hardened case and using it as a camera would be OK, but you might want to keep your camera running while you use your phone for other purposes (GPS, actually calling someone, listen to music...), and you wouldn't want to lose your phone in the middle of a mountain.
Putting you mobile phone in some hardened case and using it as a camera would be OK, but you might want to keep your camera running while you use your phone for other purposes (GPS, actually calling someone, listen to music...), and you wouldn't want to lose your phone in the middle of a mountain.