You are disagreeing with the conventions of war themselves. The minute the elves invaded another's territory, then they ceased to be defenders and became agressors by the very definition of the word.military campaign in history has been justified. That still doesn't change the definition of words and how they apply to people and actions.
A person who beat up someone who entered his house uninvited is defending his proprierty. But if he pursues the enemy until its own house, then he becomes the one guilty of breaking and entering.
If the Dalish are trying to prevent a nemesis from taking away their freedom to worship the Creators or follow their elven customers by making certain they aren't in a position to harm them again, since Orlais is a nearby nation that shares borders with the Dales that can't simply go away into a distant house where they won't cause the elves any further harm (as per your example), than it's quite a different matter.
Of course, I think we're diverting a bit too much away from the original topic at hand, which is supposed to be about the leadership of the templars now that Lambert has gone missing.