"A gun is a bit too lethal."
Horseshit. A sword in the gut is just as lethal as a bullet.
"I can't even ise it as a threat."
No shit sherlock, its not supposed to be a threat, its supposed to be a tool to save your fucking life. A random stick with paint and crystals glued to it isn't threatening either, but people in this world have learned to fear shit that doesn't look like a weapons, but acts like it. You could wave around a non-magical stick with paint and crystals glued to it and get the same result from them, at least for a little while.
"I can create a gun, but things like gunpowder and calculating chamber pressures are a pain in the ass."
Are you too stupid to understand metallurgy or the principles required to build an airplane too, asshole? Firearms were invented hundreds of years before airplanes. You made a MAGIC FUCKING JET ENGINE, get it together you hack.
The author is basically saying "guns are too dangerous/immoral, but its fine if I give a sharp object that can cut through anything to a robot that has already demonstrated zero appreciation for the value of human life."