To convert your image to what it represents:
A man shoots another man in front of a crowd of people and a cop.
A cop sees this and does not shoot or arrest the man that shot the other man.
The cop opens up the police arsenal and starts handing out guns to the crowd of people.
:think:
No, that is just stupid.
In reality, the situation is this:
A man pulls out a gun to shoot another man.
There is no cop anywhere nearby.
There is a crowd of people watching this.
If the crowd of people are unarmed, they can do nothing but run and get shot in the back while trying to flee the man with the gun.
If there are some people with concealed carry in the crowd, purchased with their own money, they can do what the missing cop is not able to do because he is not there, and they can try to stop the first man with the gun before he kills all of them.