So is a modern sniper evil? He trains long and hard to kill people in cold blood, who are unaware of his presence, outside of actual combat. No fight. Kill. And not in battle, but to stalk hopefully important enemy officers, specialists, etc, and zap them when the least expect it.
So the grunt who triggers an ambush and shoots back is less evil than a sniper?
Is firing automatic weapons at the enemy in the village in an active battle less evil than waiting and sniping an enemy as he leaves or enters a village? Or walks to the outhouse? The "honorable" way is much more likely to get your people and civillians killed by complete accident.
I really think the Evil requirement only makes sense if you have to kill an innocent to get into the guild. Just knowing how to kill sneakily is hardly more evil than killing openly. Whom you kill is far more important than how you kill them.
In this Marine's humble opinion, anyway.