Then explain why (as an Assassin in the game), you can kill literally every single guard, even when it is not necessary to infiltrate the area and get to your target, and there are no consequences or criticisms for it?
Because gameplay and story segregation is a thing.
"Mistakes are just a part of learning. You donít become an Expert At Bandit Extermination without accidentally offing a few farmers, for instance."
The Assassins are psychopaths who kill innocent people without remorse in the name of some vague notion of "freedom" without ever really explaining how they would run things differently than their supposed enemies. Seriously - can anyone here name any specific differences between the Assassin and Templar political philosophies besides vague platitudes like "order", "control", or "liberty"?
All those city guards you assassinate in the game? Those guys aren't knowing participants in any conspiracy - they're just regular Joes who took a job guarding a building so they could feed their families. They're essentially cops when you get down to it, and you murder them by the thousands in the game and at no point does any member of the brotherhood show any regret for it. Even the Assassin motto "nothing is true, everything is permitted" reads like a passage from a psychopath's diary. They're literally saying that ANYTHING they do is justified in the pursuit of their own goals.
The Assassins and Templars are little more than rival gangs fighting over territory when you take a step back and really look at the situation objectively. The only difference is that the Assassins leave a much bigger trail of bodies in their wake.
I think Assassins are fighting for a world where peace is achieved through freedom. Their goal is merely to remove the possibility of peace being achieved through controlling people and do so by eliminating templars. Once the templars are gone, the assassins would presumably disband and assimilate into society.
Their motto is an embodiment of the assassin's ideal: freedom. To permit everything means for man to be free. For nothing to be true, means no one standard or ideals can be placed among men.
Assassins regret killing in order to achieve their means. But such is the nature of life when peace can't be achieved through mutual understanding.