Harry knew that his idea to get the rebellion to surrender wasn't going to end perfectly, but he never even fathomed that the final holdouts had some sort of death wish. Though, seeing them leave Pureblood sympathizers from the war impaled on stakes until the trapped birds had their fill of the corpses should have served as a warning. Bob had suggested sleep deprivation and targeted whispering to disrupt their mental states and to sew dissention into their ranks. It sounded too much like mistreatment of prisoners to Harry, and that's when he realized he was essentially in a protracted war.