Holy crap, a lot of veterans in here are totally blowing up over something that's not an issue.
FSO has never guaranteed sides. They are very accomodating, but the plain and SIMPLE fact is it has ALWAYS been such that if you're needed for allies, you'll be placed in allies.
They are very accomodating on the matter, but when it happens you better not blow a nut or pop a vein in your forhead about it. Honestly, nothing I've read has ever suggested otherwise about the FSO setup.