And how was it this individual got in close enough to reach for your sidearm? Because he wouldn't get in close enough on me - if he was up in my sh**, he'd have a muzzle pointed at his gut.
Welcome to the forum. People get this close to us everyday. Standing in line at the store, sitting in a waiting room, drinking in a bar, church and so on. Granted these places do not generally lend themselves to someone attacking you but the odds work out about the same as being on the street.
Yes it would be great to say "No one gets within 6 feet of me" but in real life it happens daily often without us even noticing. This area around us, 0-6 feet, it what is known as "THE HOLE". It is not a place you want to be if you have to defend yourself. Your opponent does not have to be a nijna, gunfighter, MMA champion or anything else. He can use whatever weapon he has available to hurt you with including his hands and he is close enough to do it.
As I and others have stated it is what puts you in fear for your life. What causes you fear may not cause me the same worry. Disparity of force includes Size of the attacker, his mental state, his claims (I have killed before and will do it again type of thing), the number of attackers and so on. Are you physically able or physically trained to defend yourself hand to hand, toe to toe with someone all the while protecting your firearm?
As to the bolded comment. It may or may not be legal in your state to draw your firearm simply because someone got close and is up in your stuff. Remember a lot of this will hinge on your state laws but not matter what you will have to prove a direct, immediate threat to you/loved ones/third person etc. in order to justify using deadly force.