The only way to kill demons is to understand what quiet violence created them in the first place, work out how to solve that problem, and turn it into a weapon. You might kill a demon of mouldy water with a purifier, a demon of poison-laced diet drugs with its own reflection, or a demon of bigotry with a pride flag.
Unless you address the root cause of the problem, the wound in the world will continue to fester, and the demon will be reborn, free to wreak havoc. To defeat the demon truly, you need to make meaningful social change in your communities and help those around you.