And before someone starts complaining about "But we didn't used to have cellphones!" no we didn't, now we do: It's called progress. One thing that has helped emergency response times quite a bit in high income nations is the proliferation of mobile phones. When something happens emergency services can be notified in seconds, and get the response rolling that much faster.
Happened when I was in a car accident. I was dazed for maybe 20-30 seconds, then got my phone out and called for help. They had fire responders on scene in under 2 minutes, police 30 seconds later and EMS in about 4. In that case, it didn't matter, everyone was fine other than bruises, but had there been something serious, it is much more likely it could have been dealt with. The only reason the response was so fast was that it was in a populated area, and that I was able to call for help almost immediately.
To me it seems like the concert issue is one of acceptable behaviour, not the phones themselves. It is using them in inappropriate ways. Well the answer there isn't "take them away" or "lock them up" it is to let people know what is and isn't allowed, and to enforce that by removing people if necessary. People can learn, it turns out, and most can understand what rules apply to what social situation and obey them. There are those that can't and you have to deal with them, but you do it on an individual basis not by something like this.