Proficient in accurate shooting, and being willing to shoot another person are two separate things.
One can adequately defend oneself if he is willing and able to pull the trigger at the right time even if he is a poor marksman, maybe. One can not adequately do the same if he is a superb marksman who hesitates or can not pull that trigger. Being willing to come out the other end no matter what is the most of it. Being a decent shot improves the odds considerably.
"A Liberal is someone who doesn't care what you do, as long as it's mandatory". - Charles Krauthammer