Kinda cringe for an origin of a creed, but it's a good rallying phrase. Surprisingly succinct.
"To say that nothing is true, is to realize that the foundations of society are fragile, and that we must be the shepherds of our own civilization. To say that everything is permitted, is to understand that we are the architects of our actions, and that we must live with their consequences, whether glorious or tragic."
Are there any similar phrases you've seen popularized by a game?
They needed the assassins to always be the underdogs, which meant that they never got to actually put their beliefs into practice. As for their politics, I don't remember them having any, because that would get in the way of all the awesome tailing missions.
The assassins were kinda made to always be incapable of holding power. Their entire role was preventing the templar's from using the alien artifacts to control humanity's development.
What I got was that they just kinda fizzle out during times when the templar's don't have control of the pieces of Eden.