The active shooter situation in Dallas -- in which five police officers were murdered -- was resolved when the shooter was dispatched with a fist full of C4 delivered by remote control robot.
According to one TV report, CNN I think, the robot carried the explosive up to the opposite side of a cinder block wall against which the killer was leaning. The explosive was discharged, and the killer was killed.
For some reason commentators are concerned about what they perceive as an ethical issue. Apparently, they think a killer shouldn't be killed unless the police officer puts him/self at risk. Some ethical issue.
News flash: By ambushing his opponents, the killer essentially waived the gentleman's rules of dueling. Or more to the point, violate the rules of decency and all rules are off.