Well, I was trying to reply to his refutation of "the use of drones to indiscriminately kill civilians", but I suppose if he was merely contesting the word "indiscriminately" he might have a point.

That is, if we believe the U.S. is making a good enough attempt to avoid civilian casualties in drone strikes, which is questionable.

He wasn't refuting that. He was refuting the air quotes around "suspected terrorists". He did not refute the fact that drones killed civilians or the teenager.