Back to productive topics though, I just had a thought that could be immensely helpful against 5C if implemented. A dedicated in-game message board built into the powerplay screen for pledges only. Organizers could use it to post orders in a place where randoms would be able to see them without having to join an external community, and if you have anyone posting contradictory orders in order to sow confusion would have to do so under their own CMDR name, so they couldn't flood the board to confuse the randoms without revealing their usernames, and flooding this message board with contradictory orders could be as frowned upon as 5C is now. This does nothing to stop intentional 5C, but it could do a lot to reduce unintentional fortification or preparation of the wrong systems and highlight where intentional 5C is in use, which would help greatly with both reducing false accusations and with people using randoms as cover for intentional 5C, effectively helping resolve the issue that spawned this thread regardless of who is correct in their accusations.
I agree, and I wish this could be taken a step further. Were Frontier willing to take a more active approach to Powerplay, I'd support integrating power leadership directly into in-game powerplay boards - it would, as you say, go a long way to discourage unintentional forts and preps, and make intentional 5c far more obvious to spot.
Sadly, this probably clashes with Frontier's hands-off philosophy for game design, if you can even call it that... Still, it's something I'd love to see implemented, in some form or another.