Even if you COULD talk to every enemy, I would not want to have even the option to do that every single time for every encounter, that would quickly drive me insane, even if I selected "no I want to fight" each time.
I agree & understand what you mean: better only for a few (or more) "special encounters" I wish to have the possibility to choose to fight or do not fight (or do that fight on a later time, when I'm, for example, ready for that fight).
Also not every time a question like "I don't want to fight, please stop" or "just leave me in peace" or whatever, but simply:
If I sheat my weapon or stop using magical spells & taking up a white flag for visual 'saying' I want peace
... (that will be a funny thing or not ?)
O, and some enemies ignore that white flag or even burn it to black
