A cure worse than the disease. Also wouldn't stop the military from building up a drone army and then someone within it choosing to go rogue and take it with them. It only ensures that no one else can stop them.
I think the parent post agreed with you and was just being facetious -- 'just ban general purpose computing' isn't very likely to be a popular sentiment on hn!
Just ban general purpose computers that allow running arbitrary unsigned code. I'm sure lots of governments and corporations would be happy to get on board that one, and many end-users wouldn't notice.