I would like your suggestion on a delicate matter involving a paper that I am reviewing. I will avoid giving too many details to preserve anonymity.
In this article the authors describe an algorithm for the (unmanned) control of a military armed drone. The work has been done completely in a simulator, but the authors show clear pictures of the type of real-world military drone they reproduced, explicitly saying that the real drone can be armed with different type of bombs. The performance of the algorithm is scored based on the number of times the simulated drone autonomously hit the target. The authors never discuss possible ethical concerns of this technology, neither they explicitly say if this technology will be used on real drones to hit human targets with possible involvement of civilians (e.g. in counter-terrorism).
My personal position is against the development of lethal autonomous weapons. Even though I have several years of experience in reviewing papers, this is the very first time I have to deal with such a problem and I am not sure how to move. I think that this kind of ethical problems are common in medical-related fields, but rather uncommon in engineering, and that they are catching our community off guard.
Note that, from a formal point of view the situation is fuzzy. Even though there has been an international petition against the development of autonomous weapons, the formalization in an international ban (like the one for chemical weapons) seems to be far away. Moreover, the ethical guidelines of the journal just apply to the use of animal in research, and to experiments on human subjects. This let me conclude that from a formal standpoint the paper is legit since it does not break any rule.
I have considered writing to the editor expressing my concerns or pointing out these concerns directly in the review, so that the authors can give an answer to my queries. As last solution I am also considering the option of withdrawing, but I would prefer to set up a dialogue with the authors and the editor since this is more constructive for everybody. However, I think it is also important to consider the hypothesis that my ethical position can bias my review (even though I am trying to be as neutral as possible) and this may be unfair for the evaluation of the technical quality of the proposed method.
My question is: how should I proceed in the review process? There are a few options: withdraw for ethical concerns, just review the article, review and express my ethical concerns to the editor (and maybe to the authors).
Update: 5 March 2020
Thank you everyone for your answers, they really helped me to better understand the situation. I decided to withdraw as reviewer, and I sent an official letter to the editor. In the letter I expressed my ethical concerns without giving any comment on the technical quality of the paper. The paper did not break any formal rule, therefore recommending an official rejection would have been like imposing my personal ethics over the review process. In the letter I have also reported those sentences that clearly framed the drone like an autonomous lethal weapon.
The assistant editor wrote me saying that the editor liked my academic attitude and wanted me for a second review. The editorial team has contacted the authors, who said they did not wanted to create a misunderstanding and that they are willing to modify the expressions. This seems to imply that they have forwarded to the authors the list of sentences I confidentially reported to the editor, and that the authors want to adjust those sentences in the revised version.
My personal opinion is that just rephrasing the paper without changing the substance would not be enough. You can substitute "target" with "goal" and "attack" with "reach" but that remains an autonomous armed drone.