If people can purely play "however they like," multiplayer functions and mechanics are simply broken, because no one naturally "wants" to be interdicted when trading, and no one naturally "wants" to be hunted when they have a bounty. Especially when people play in Open, the mentality of extreme individualism is detrimental to the game, not productive.
There are plenty of limitation and stipulation as to how the game should be played, just because players are enacting certain parts of the mechanics don't make it automatically illegitimate.
https://www.elitedangerous.com/en/gameplay/combat
I can think of few things more detrimental to a game than trying to force people to play against their will. And there is nothing special about open, except that you can play alongside others without joining a group. That is all it does. Nothing else is required.
As for the advertisement, it isn't a contract, for multiple obvious reasons. Making it irrelevant to any claims of 'limitation and stipulation'. It tells the player what they can do, not what they must. Can do, assuming that anyone else wants to play their way.
If you want to set 'limitations and stipulations' beyond the contract with FD, do it in a group. And stop pretending that 'open' mode is subject to imaginary rules...