Like you mention, I think it is far more important that there is healthy conflict resolution instead of no conflict at all. I think children seeing that it is normal to not always be thrilled about everything the person you share a house and life with is healthy. What isn't is when someone reacts poorly.
My 6 year old daughter once went and told my husband "Shame on you" when his behavior was clearly out of line on one occasion. It actually made me happy that she understood normal fighting and not okay. Sometimes she will say funny things like "You two calm down" which always lightens the mood a bit for everyone and helps us realize we are getting worked up.
I think it would be far worse to live in a house where nobody ever talked and there was a fake happy feeling. I want my daughter to understand that real life can be messy, but you can choose how you respond.