You've completely missed the point of what I've been trying to say.
I am not debating who is good or evil.
I'm saying if you're going to label Arthas "innocent" or "good" based on his "greater good" rationale (killing innocents to save something precious) then the same standard applie to Sargeras.
I personally think that Arthas was bad, as I personally think Sargeras was bad. But I'm not arguing who is or isn't bad, merely that their actions are so similar (differing only on scale, i.e. cities instead of worlds) that if one is bad so is the other, equally if one is good so is the other. The person i've been debating with is trying to say what arthas did wasn't bad and entirely justified but what sargeras did is bad and not justified - with no good or logical explanation.