In Ezio’s (and Altair’s) world, mercy is for the weak and hesitation will only get you killed. This is ASsassin’s Creed after all, and you need to be able to take down your enemies, no matter how large the number, without a blink of the eye(s).
The latest trailer for Assassin’s Creed: Revelations makes the game appear to be more ruthless and violent than any of the games in the series before it. Having played the first two, that says a lot. Ezio is out for blood this time and he will not hesitate to take down anyone in his path.