Certainly I agree that Open would be far less populated if it was the actual ultra-violence zone of forum legend, and that the majority of Open players are there for non-PvP socialising.
That it's not that ultra-violence zone and that it remains popular might tell you something
However (is it a nice house?) that's not why we don't have an Open PvE mode. We don't have one because it's impossible to make one that's actually satisfactory.
Let's take station-ramming as an example. We've done the easy bit of the PvE rules: player weapons have no effect on other players. Now, what to do about collisions?
- collisions do no damage but still transfer momentum: griefers ram their victims around the docking bay until they die
- collisions do no damage and don't transfer momentum: griefers use cheap (but immobile) Sidewinders to block people from taking off or landing until their timer runs out and the station kills them
- collision detection between players entirely disabled: griefers use Sidewinders to fly inside big ships before opening fire and using them as ablative armour. Also looks really silly.
- ...any other options?
In all cases, you're not dying to a player, you're dying to the environment in a way that's equally possible (though far less likely) if there's no players about - I lost an Eagle once while taking off from a station because some NPC Beluga was having difficulty leaving and I passed between it and the station guns at exactly the wrong time. Boom!
(And that's just one scenario to cover)
Mobius (or FleetComm, or whatever) works because it has human moderators who will assess whether what you did was actually PvP. An automated system can't do that - it has to use a set of fully objective rules which either disregard context entirely, or are made more complex through sub-rules which try to pick up on context (imperfectly).
This gets on to your "the solution to bad rules is better rules" point. That only applies if you can make a set of better rules. In real life, we don't. In real life, sticking a knife in someone with intent to kill is legal in some circumstances (e.g. self-defence) and illegal in others. There are rules about which circumstances are which, but they're not ultra-specific "cover every case" rules: they're guidance and principles to be interpreted by trained human experts, who may themselves reasonably disagree, and who may take months of examining evidence and arguments from other trained experts to come to their conclusion.
This is the right approach, because otherwise we'd still be in sub-committee hearings on exactly which circumstances murder was illegal, and wouldn't actually have got around to outlawing it.
But it's not an approach that can be used in-game, because we don't have time for a full legal process every time someone boosts out of the station without looking where they were going.
Going back to the Gnosis, here are the relevant rules:
- opening fire in the No Fire Zone should be a crime
- loitering and blocking landing pads should be a crime
- criminals killed with detected crimes should be punished
- punishment should include transportation to a detention centre to make immediate reoffending harder
In "normal" circumstances there's nothing wrong with any of those rules.
There is *no way* that anyone writing the crime rules back in 3.0 would have thought to add "unless the crimes take place as a result of a Thargoid attack spreading shutdown fields around a megaship over 1000LY from the nearest detention centre", and it's completely unreasonable to have expected them to. And there's not a *huge* amount of point in adding a specific exception for it now, either, because that specific case is unlikely to come up again, and that exception won't help with the next weird edge case.
Obviously a real prosecutor would have ruled it not in the public interest to prosecute in that case, even though laws were technically broken. The laws aren't the problem - it's the rigid interpretation of them which is the problem.
But with the scale of the game, instant robo-justice is a requirement. And that means that "better rules" isn't a practical solution.