If you are at the point in the game where you are ready to be at war with every other civ in the game, then either don't sign a non-aggression treaty and just finish the game, or wait a few turns for any you did sign to expire before completing your domination.
So not automatically push you into war with everyone then. It shouldn't be anything like so absolute. But nothing wrong with making it so they don't trust you as much if you're a known pact-breaker. It'd be nice to see a fairly small 'base' penalty that was then modified by other things:
* Ideological differences between you and the guy you broke the treaty with should reduce the impact - a good guy betraying another good guy would be frowned on far more than a good guy betraying an evil guy.
* Ideological differences between the 3rd party and you. Good empires should dislike bad guys who betray people more than they dislike other good guys betraying people.
* Ideological difference between the 3rd party and the guy you betrayed. Once again, there'll be less bothered that the other guy got betrayed if he's a different ideology.
This should mean that the impact of your treachery is hard to predict across the whole international stage. It makes choosing to attack before the pact ends a gamble; there'll be diplomatic consequences which might prove painful, but might not. It makes it harder to predict specifically how the AI will react, but not hard to predict generally what they'll think about it.