There are no rules at all in Open. How can you describe this as 'consensual'? Consensual always requires an agreement to a certain rule set. Now, redefining this to 'agreeing to no rules at all' is a prime example of how the truth can be distorted beyond all recognition. If you look at the term 'consensual' outside of the game context, there's usally the word 'law' involved. For a reason, don't you think so?
Or lets try to approach this from the other side. If what you say would be true, and if we agree that the term 'non-consensual' exists, what would be an example of non-consensual in your world? Why would we need such a term AT ALL?
Quick side note before I go on: I have zero knowledge about Black Desert Online so I'm sure I'm missing a lot of context.
First off, there are rules in Open Play. From the game mechanics themselves to the BGS, crime and punishment, and everything else the framework of how Elite is played is created. Whether or not this satisfies you is a different question, but you absolutely can't say "there are no rules at all in Open." It's just like chess, where you have a board, black pieces, white pieces, and all the things that dictate how those pieces can be used to successfully play chess.
I don't have to go outside Elite to provide an example of non-consent. Don't want the possibility of PvP? Pick Private Group or Solo. Job done. You've successfully not consented to PvP in the context of Elite: Dangerous.