Sunny, a no-fault law says to married people that there's nothing wrong with being unfaithful, because there's no punishment for it. That's a problem, in my mind. An at-fault state penalizes the person who has an affair or otherwise misbehaves toward their partner. I think that's the way it should be, and I know that's what made my H at least think twice about separating.
Painter, this goes back to legislating morals. My incentive for being faithful to my H was never legal punishment.
I don't believe for a second that Mr P would have been faithful had we not lived in a no fault state. That wasn't on his radar screen at the time.