We don't have to see them killing to know they've killed innocents before. You don't join up with glorified bandits to help the poor and unfortunate. They're just gonna come back, probably as part of the enemy empire. They need to die, womp fucking womp.
Pardon me dear sir or madam, I cannot help but to notice that you have quite rudely trod upon my territory. As a retaliatory response I'm afraid that I, and the rest of my kindred, must now sting the ever loving shit out of you.
Ever so sorry.