The only difference is that non-nexus neutrals essentially never raid fort and if they do they potentially can get marked hunted by fortress such as Akedeh.

Other cabaled neutral characters might have a reason to fight individual fort members i.e. battle v fort mages, outlander v fort dwarf, etc but those are individual fights. But, outlander doesn't really come and raid Fort to just to try and kill a Fort paladin for example. And, those fights are known before hand, Fort mages know Battle members will be gunning for them and if they see them a fight is going to happen. Its not like Nexans that you can't attack because they MIGHT not be coming to murder you.

But with nexans the fight potentially comes whenever light tips and they will continue the fight to the point of raiding the cabal if need be. To me that is akin to declaring war with the Fort. I understand people have different points of view, but for me it's hard to see how a Fort character turns around forgets recent history after a nexus raid. I could see Fort players forgiving nexus of their transgressions or reconciling if nexus was contrite about their actions and then moving forward but I don't think that is going to happen. :p