First, in most states it is not legal to point a weapon at someone unless you are in a situation where you're legally allowed to pull the trigger. That is, you are legitimately in fear for your life. In that situation you will likely have very little time to act in self defense.

Second, racking a slide is an action that requires fine motor control. Under the pressure and adrenaline dump that accompanies a life-or-death situation, fine motor control goes to crap. If you are fumbling with your pistol, it's useless.

Third, if you don't feel comfortable with your ability to safely handle a loaded gun, you probably shouldn't be carrying at all.