There is nothing lower than an informant.
and at just what point is an informant a good thing when someone is being assaulted, battered, robbed, being beaten, when someone is being killed, after they are dead?
Any reasonable person would say long before any of that happens. As in when you first notice something out of the ordinary.. like a drunk guy with a gun... If you want to put yourself and others at risk by allowing something so ignorant to go unchecked, have at it, however I certainly hope any reasonably minded people here will recognize that the time to intervene is when your gut tells you. I would rather call the cops for a false alarm than hold a dying loved one in my arms because I was too ashamed to tattle.