I think it's appropriate to have a talk and try to be reasonable, logical, and understanding.
I don't think a partner should be afraid to speak up if a certain type, or quantity, of porn makes them uncomfortable, and the watcher should listen and understand why. For instance, if a partner thinks it's a gross genre or how the people look triggers insecurities. I think talking honestly and openly can help.
And I agree - never lie about it. Don't pretend to quit and just hide it. I know a lot of relationships operate that way, but what a crappy way to have a relationship.
If a personal has some kind of moral opposition to porn and feels very strongly, it might be a dealbreaker or perhaps a sex therapist could help the couple be able to understand each other's position.
And I agree that a person can have an "addiction" to porn that can really be a problem beyond anything normal.
Sure, I think someone could theoretically "quit porn" if they wanted to. If they, you know, actually wanted to.