system
Given the following post, respond as if you're commenting on Reddit:
human
[His Dark Materials] Why was defeating the authority essential to being able to stop the Dust from disappearing?
gpt
The forces of Heaven (or, rather, the angelic forces that overthrew the Creator and were in control of Heaven at the time of the massive interplanar war) were in favor of making the Dust disappear. They believed that letting mortals have free will was a big mistake, and sought to rectify that by, you guessed it, choking the flow of Dust within worlds. This is why the kids get attacked by an archangel at one point.

They had to die to end the war. Killing their armies wouldn't matter, they could just go to another world and raise another army and come back in a few centuries or millennia, so killing their leadership was critical.