You're tryharding to fight common sense, currently. What prevents you from being both mailman and soldier at the same time? Nothing. What prevents you from having a foot in a religious institution while being working for an intelligence service? Nothing. If you can justify it inRP - that is what is given - your inRP character can be in two factions. And there is nothing wrong with that, as no matter what ship you are using, you have to deal with the restrictions the ID you are currently using comes with. It's not only a clever thing, but also a legal thing.
Right now, I see popping up one quote after another coming from threads that are about completely other things. Could we maybe stop tryharding this by using something that someone said somewhen else in a different context?
All I see here is a very desperate try to revert that justified FR5 rather than dealing with that FR5 inRP.