No, it's very simple. I've broken it down several times in this thread, I'll do it once more.
Open PvE will come with severe drawbacks. It'll be a shining red target in the starting menu for every griefer to aim at. You will not get away from harassment to the same degree that you have in Mobius. There will be problems and troublemakers, and it will occur frequently. Many people speaking in support of this option have accepted that inevitability and said it's still worth it simply for the convenience and to draw more players in.
So if you can accept that level of risk, then it's reasonable to assume that you can also accept the risk of moving back to open if the rate of PvP is significantly decreased through your own efforts.
IF you chose to go back to open you have the largest group of players under one banner in the game. Period. By orders of magnitude. If 10% of that group decided to work together towards a common goal you could have significant influence in the game. First and foremost you have the ability to attract people. The first people you're going to attract is going to be the pirates, naturally. That's fine, because being the largest player group means you will have no problem attracting PvPers under your banner. Having your own security will reduce the rate of PvP as long as you keep your own PvPers interested in providing assistance. That comes in the form of them being entertained, so the important factor is to have someone competent organizing the PvPers. When the pressure lets up, they've got to start applying pressure of their own and spread the zone of influence until they have difficulty maintaining it. If it's challenging, they'll stay entertained.
Now you have a zone of influence in which the threat to the PvE players is significantly reduced, and they can do what they wish. If they wish to do so outside of the zone of influence that can be done one of two ways. Reputation and assistance. Reputation comes from being consistent and decisive in allowing your PvP members to commit to retributive actions. If people keep getting blacklisted for harassing your members outside your zone of influence, they'll stop harassing them, and thus your zone of influence spreads. Etc and so on....
There is a very large and popular group of players in many other games that functions on this same ethos, and has been very successful for years now. You may have heard of them as GoonSwarm. Their dirty little secret is that they are not a PvP primary gaming community, not even in Eve Online. They are PvE primary and the PvP side is just there to facilitate that.
It only works AFTER you have a large group of players, because only then do you start to draw enough attention, and thus create enough content, to keep a small section of PvP oriented players busy.