It's early, i've had half a coffee, so this is my take on the 'solo or open' issue; and to be clear this is not just about ED, but ALL computer games that do MP.
The problem has always been (going all the way back to MUD in the 1980's) a 'cultural' issue in relation to the empowerment of 'anti-social' behaviours, the rewards and encouragement of them and the style of game design that developed around that.
Now if your game is fully setup to be a pure competitive darwinian fight, that is a perfect vessel for such MP gaming, everyone is on the same page and knows what is expected of them and what to expect. These are historically games i've always found a bit boring as they are generally shallow by design because the rules are simple, kill or be killed. Fun for many people though as MP FPS games can become big financial hits.
The problem for ED (from the outset) is it tried to allow that MP'rs could also be decent civilised and culturally mature individuals capable of showing restraint and able to 'role play' their place in the ED world and build that worlds narrative. I think in hindsight we could say that was naive thinking. The DNA and history of MP gaming has seen generations (now) of people born and raised on a different type of MP game, and that has nurtured a 'type' of MP'r gamer that has zero interest in any of that restraint or world building, they just want to gank for the Lolz.
It is possible to design rules into the game to force them into the preferred behaviours (and ED has some of that), but this type of MP'r has so many choices to turn to if you drive them away too hard, so it is a difficult nut to crack. You are talking about needing to change the learned culture of the majority of MP'r gamer's, and heck there will be a large number that don't want that.
So in the face of that near impossible problem to fix, it has been my perceived wisdom going on 30 odd years now, that except for light distraction gaming (in a game i care little about, or wish to not invest too much in), i keep away for MP games. Elite has always been a game i cared about, and so far in ED (just a few noobs days worth mind you!) i still care, so i play Solo.
EDIT:
Now to address the OP's suggestion, to 'turn off' PvP mechanics in Open, keep in mind in the game we fly spaceships that get damaged and cause damage when we fly into things, we also have lasers and missiles.......so yeah. You don't want to break the internal logic of the game (too much).
You could have laws and enforcement of laws (as we do in real life). You could make a pirate player really feel the sweat on the back of their necks each time they tried to enter a system with any kind of law enforcement, you could enforce massive financial penalties, ship impounding's etc for all manner of crimes. You could in effect have a strong and robust crime and punishment system that would aid both the MP (antisocial gaming side) and game world building, but you would also expect prams to be pushed over and lots of doll throwing. The question becomes would the MP gamers want to play in a game where they have to face up to their in-game choices?
