It still leaves the problem, alf, of when the navigational accuracy of the FMS/Map is suspect - eg INN, where only 1 DME is available for a 737 Classic to obtain an update on position in the valley - ie it cannot update, and the FMS position will 'wander' towards the INS position, which may be far enough away from reality to assume a mountain where one does not exist. All the clever terrain maps/call-outs are of no use if the a/c does not know where it is. Thus the VMC over-ride option is required.
Once we get to a state where the nav accuracy is practically guaranteed then I agree with you.