Vader took part in blowing up a planet.... because they wanted a 'demonstration'.
Exar Kun? oh please he wiped out the last of the Massassi race to become a spirit, he led the assault on Ossus, there were no lengths that Kun would not have gone to, to become ruler of the galaxy.
Bane is different yes.... oh wait, the Thought Bomb.
Bane. Yes did his thought bomb kill innocent people? No, it took out sith in his way and his enemies, Jedi.
They all had weapons, they were all combatants. Fail to see the issue with what bane did.