I think I understand.

[He pauses.] But do you know your quarry? Who are you taking vengeance for? There's a difference between vengeance and justice, as well. The first is a dark thing that leads to a path i've seen my brothers tread, justice is cold, clear, and has an end to it.

We can't build anything from vengeance, it undermines the very foundations of the world, but justice props them up.