Why does everyone treat fights/arguing in a relationship is normal/expected?

It just feels wrong. Especially when there are things you can do to avoid it and being honest eith eachother and open minded can do a lot of work. I don't know why people treat that as a normal thing and just expect it in a relationship. I've never fought in any of my relationship, I never fought with any of my family either. I've had "discussions" with my brother that might get loud but at any moment I can just say "wanna get food" and it's over like it never happened.
Why does everyone treat fights/arguing in a relationship is normal/expected?
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