Hussar
Legend
Umbran said:"Necessary" is like "never" or "always" - it is an absolute, with no room for compromise. So, is the threat really necessary? Probably not. I myself have played in games that haven't had credible threat of quick death, and had fun.
But don't take it the other way, either. Hammers are not completely indispensable, but most toolboxes have them. The threat of death is a useful too, and like others used judiciously it often works wonders. Of course, there's occasionally a case where it isn't the right too, and they, of course, you shouldn't use it.
Umbran for the win. Excellent point. It might be better to say that death might be a consequence some of the time, but, not always. Thus, it's not absolutely necessary, but, it's another tool in the DM's toolbox.