It seems pretty clear that the immediate cause for this near tragedy was that there was a clear failure of the people in charge of security to act responsibly and intelligently.

That's what needs to be addressed urgently. No point in going off into a panic spiral about all the things that haven't happened and might someday happen but very probably won't.

Remember we are all far far more likely to be killed in a road accident than by a suicide bomber. That doesn't make us all stay home to eliminate the risk, we do what we can to reduce it, but accept that there is always a risk in anything we do in this world. And if we did stay home to avoid it, that'd increase our risk of an accident in the home, which is where most of them do happen anyway.

Don't forget - "You'll never get out of this world alive".