I think an issue with this reasoning is that "protect the weak" and "be just" are things that many people (admittedly not all) from "both sides" _do_ want to do, and that reality is often not so straightforward, involving tradeoffs that cannot be objectively evaluated as "just".
Personally I believe that a lot of disagreements in this realm come down to misunderstanding, in which case it's very sad to have to resort to destruction, when better communication and efforts to work together could create agreement or at least compromise. Admittedly resolving these misunderstandings is really hard, and I think a lot of us don't have the skills or tools to do so in a reasonable amount of time.