By removing the political risk that comes with sending soldiers into battle autonomous weapons lower the threshold of going to war and thus threaten world piece.

Thousands of experts, including Elon Musk and Stephen Hawking  have called for a ban on these weapons and Elon Musk has in fact warned that international competition to AI superiority is the most likely cause for World War III.

IIIM has also been very vocal on this issue and taken measures to work towards ethical use and development of AI.

This video, narrated by Stephen Fry, gives a disturbing insight into the issues at hand.