There, we find ourselves at another crux. As I have stated, the Council had many flaws, and I still do not agree with how the Order handled many things. They considered some things to be an act of the darkside, and other things not.
To use more examples; I carry with me the responsibility of tragedy. What I did, I will be responsible for for the rest of my life. Does that make me Sith? I cannot answer for sure, only that until I join the Force I must face my choices, live with them, and never repeat them again while serving the Light.
Alak, one of the friends I spoke of, fell. He did as you stated. He killed hundreds. Thousands, even when he bombed Taris. He did so with hate in his heart, and his desire to destroy. He became Sith, and even the Council agreed he was so.
The Order was never in full agreement on one sort of punishment. We had no justice system among ourselves, those who fell were fallen and little was done about them. Alek never saw justice except when he died. The Council wished to punish me, both in exile and later on but while I agreed it was just at the time I also felt angry for their actions.
Which may or may not answer your question. If it sounds the like the ORder is hypocritical, and has an odd definition of justice you would be correct.