It depends on what we mean by "fight" --- to never disagree about anything, is suspicious, that either neither of you have any strong opinions or principals about anything, or that one or both are suppressing any differences and ignoring their real feelings. Now conflict in the sense of exploring and dealing with differences and disagreements, is not a bad thing, so long as we handle it fruitfully and not unpleasantly. By "fighting" I did not mean aggression, but exercises in assertiveness. As Kat says, what's important is the degree of control, and, I'd suggst, the quality and usefulness of the outcome.
Anyhow, thanks Ltd, for reminding us that I said that "fighting is NOT compulsory", meaning that it's absence isn't a dreadful thing.