They will be when our robot overlords want to get rid of us. :-)
This assumes robots would want to be friend with each other, because robots. They'd probably wipe each other out very efficiently too and they would probably be able to do it without the use of weapons, it would just be cyber warfare.
No weapon in the history of mankind has ever been perfect.
Loads of things can be used as inefficient weapons, for example we could be worried about rouge states developing methods of dropping dead cows from zeppelins.
You jest, but launching dead cows from catapults was indeed a medieval siege tactic.