Can't kill people?
At this moment, Ji Jue held the Bone Knife in his hand, and far from disliking it, he almost wanted to lean in and plant two kisses on it—wow, I never expected you to be such a considerate little treasure!
It's better if it doesn't kill!
What era is it now? Who still uses knives to kill people?
If you have a gun, use a gun; if you've got a cannon, fire it. How many can you kill with a knife?
Moreover, if one stab kills a person instantly, that's when the real trouble starts... dispersed spiritual energy, collapsed Matrix, blessings returning to the Superior. Each one would be a mess to deal with, and in the end, hardly one in ten would remain.
If it didn't kill, then there would be no worry about destroying the material!