Such an absurd and unnecessary waste of life.
I know there must have been thousands of ways to disperse the crowd without killing anyone... and with their level of mastery over magic, it wouldn't even be an effort.
But they chose to kill all those civilians... innocent people that just want to be witnesses to an event.
The author taking a few panels here and there to show the people deciding or not to go see the concert really drives it home that... they are people, they were scared but curious too, there is an event that can change the world around them again, and they want to bear witness to it... doesn't mean any of them are ready or deserve to die for it.