Movies sometimes get this thing right though. Don't forget that Dr. Strangelove pretty much turned out to be a documentary!
So your answer is, "Sure, let's weaponize brains, nothing can possibly go wrong"?
We already weaponize brains.
However, we mostly only arm brains that have an IQ of <120 and some human values baked in (e.g. empathy to other humans and living beings; a family to protect, or dependence on other social structures that demand pro-social attitudes).
Well no, mostly we don't, because the brains who happen to be the weapons still need a world to live in after they fight. The difference is that with artificial brains, hey, why would they give a crap what comes after the killing?