Most of Ariana Grande's fan base are teens and pre-teens, so imagine what the events of yesterday have done to their world view.
When I think about how much life has changed in the 40+ years since I was a teenager...I never worried about a classmate bringing a weapon to school and using it on the students. I never thought twice about going to a concert or sporting event and worrying about a suicide bomber wrecking havoc on attendees. A passenger could walk onto an airplane without going through security, etc., etc.
Thirty years from now when my 3 nieces are in their 40's and 50's, what will their world be like?