You answered your own question right there.

Unless you KNOW how to handle a weapon, in the dark, in a confined space against an unknown attacker (or attackers) the chances are you are going to have it taken out of your hands in about 2 seconds and turned on you. if you did manage to get a lucky shot in there is a very good chance you would kill them...in which case YOU are going to be in the shit.

Its nice to think we could all defend ourselves but the reality is a lot different to that.