Much of Sirrurg's early work was indeed hunting the dragonslayer cults, which is why the dragons (even Big D) gave him a silent nod of approval. It talks about this in Dragons of the Sixth World, I believe. At any rate, Sirrurg's actions had always been at an 'acceptable' level until he wiped Cali off the map, which springboarded the whole dragon civil war, as well as nations rushing to make anti-dragon weapons. A similar example in real life would be the 9/11 attack on the World Trade Center. Al Qaeda had been a threat for decades prior to that, but their actions had always been something that weren't on a level to galvanize a massive response from the American public. Sure, bombing a couple barracks or a ship is bad, and we lobbed some cruise missiles at some of his favorite stuff, but it wasn't until 9/11 that Americans decided they were going out for blood. That attack was so over the top, so horrific, that everyone stopped and said that was too far. It didn't stop terrorism, naturally, but it made everyone want to take the fight straight to them. When Sirrurg wiped out Cali, the same thing happened, and the only reason the other dragons acted was to keep one of their own from being butchered by Aztlan.