How does that negate the definition of a leader? A leader leads. There is nothing in leadership that dictates what a leader should lead by. He can lead by his lowest or highest inclinations.
If he can persuade idiots to follow in his wake? He's a leader. Not all leaders are good leaders.
I guess we should agree on what a "leader" actually is for this discussion---here's a comment I like:
Peter Drucker famously stated that when "management is doing things right, leadership is doing the right things."
Great leaders possess dazzling social intelligence, a zest for change, and above all, a vision that allows them to set their sights on the things that truly merit attention. Not a bad skill set for the rest of us, either.
It is the job of leaders to develop a vision—establish what matters and articulate why—set direction, and inspire others. Recent research on the skills leaders need establishes the increasing importance of inner resources of the psyche such as self-awareness and self-mastery.