I voted differently earlier, but on reflection have changed my mind.
I play open. I've had a few 'I wish I had my brown trousers' moments, and I've done the same to a few CMDRs in conflict zones.
However, the basic thing to understand is that people's motivations for playing the game aren't the same as yours or mine and they may not wish to play the same game in the same way that you or I do. For some, perhaps being attacked in open is not fun. An openPvE mode would render the Mobius private group obsolete, and would reduce the drama on the forums that appears from time to time when someone infiltrates the group and attacks unwitting CMDRs. It would make no difference to players in open, and would probably draw good numbers of players from solo.
OpenPvE already exists in the form of Mobius. Adding a mode that actually enforced the "no PvP" ruleset without relying on an honour system wouldn't change anything for players who don't play in Mobius. Therefore, I don't see any merit in the recent threads against the idea of openPvE. It won't change your game, so why are you so keen to enforce your game on others?