Killing those who disagree with you is wrong? In a just war people are killed and it is not a sin. Perhaps your religion reserves the death penalty for murderers. That is not the current view in the United States (treason for example). The Catholic Church, as far as I know, does not say that the death penalty is intrinsically evil if it is used for non-murderers.
Killing those who disagree with you is wrong! What kind of world do you live in?
Treason is a fine reason for the death penalty. The ruler does not bear the sword in vain. But treason is much more than a disagreement.
People die in war. That is what happens.
But I will stand with Luther and condemn Pope Leo X and any Catholic that agrees with him. "That heretics be burned is against the will of the Spirit." Why would we need to debate this?
You can have your rationalizations that you are doing it for the greater good. You can bemoan the fact that Martin Luther wasn't burned at the stake. You can try to confuse the death penalty by the state with the burning of heretics, but you are wrong and Pope Leo X was wrong.