Of course violating EULA of a private server should lead to being banned. This CG was created without a built in way to counter the Federation expansion, which led to the current events. Imperial pilots needed some way to stop the expansion, since they disagreed with it, but no counter CG was available. The 13th's blockade was a good idea for Open, but invading Mobius was dishonorable, and against the spirit of a PVE private group. If this CG was supposed to be stoppable, then why was no counter CG created for the Empire?
This was a mistake on FDev's part, which created this unfortunate circumstance. As a Mobius player, we have the option to contribute to CGs just as Solo and Open players do. Not all those who are in Mobius do though. This was built in by FDev, like it or not, the mechanic exists. Now FDev needs to step up and create equal goals so that private groups, and solo players are not such a threat to the Open players. If you purchased the game, you should not be blocked from taking part in the game's content. If your work is being undone in Open, why is that? Is it because the CG is so one sided that simple acts in Private and Solo can unbalance it? If so then the creation of CGs need to be revisited, so that some semblance of balance can be reached without players invading private servers in an attempt to change the outcome. Using the BGS to lock down the system was use of existing mechanics, and if achieved purely in Open, then that is fair play. It wasn't though. It required the use of dishonorable tactics, and the breaking of an honor code. So the lock down was lifted. Play by the rules, or be banned. It is simple.
As a final thought, FDev really needs to consider doing as they did in Damaro, and set a goal for both sides, then see who wins. Regardless of Open, Private, or Solo. That would avoid problems like this. I was trading on the edge of known space when this whole fiasco went down, and couldn't care less about the CG, as it was Federation only as far as I was concerned.