Leadership involves having the ability to guide, influence and coordinate a group of people toward a shared goal.
Ethics is basically what is good and wrong and how people ought to act. Combining these two, leadership roles cannot exist when the leader and the members do not how to act and differentiate from what is acceptable and what is not, the party will fail. The leader should be able to make not just morally right decisions but decisions that benefit most in the group. The ability to make these hard decisions is what separates a good leader from a bad leader.