Lets also not forget that the Templars started the war in the first place. Had they been more reasonable the war would have been prevented and much would be different. The Divine would still be alive and Corypheus would have had a much harder time enacting his plans.
One can just as easily say that had the mages been more reasonable and remained in the Circles, there wouldn't have been a war.
Ultimately, actions have consequences and if you push people against a wall, they will push back as the pro-mages see fit to remind us on a regular basis.
Fiona and every other mage knew that a declaration of independence would lead to a war. They still went ahead with it. Therefore, they may not have oficially declared the war but they accepted it as a consequence.
I'm sure that you could point out how the mages found the alternative unnaceptable and thus were forced into war. Just as I could point how the Templars found the alternative unnaceptable and thus were forced into war.