In Revelations, Altair and Ezio were both asked if they ever regretted being an Assassin.
Altair responded to Al Mualim with “How could I regret the only life I’ve ever known?”
Ezio responded to Sofia with “I do not remember making the decision myself. This life, it chose me.”
Both Altair and Ezio are known as the greatest mentors of the brotherhood, but they never freely chose to be an Assassin in the first place.