The distance restriction to be sure you can avoid having to grapple is more like 21 feet, not arm's reach. Inside that distance, a reasonably fit person can get hands on you before you can get your gun deployed effectively even if you have already identified them as a threat and are watching when they start their run at you.
Realistically, one needs to have some sort of plan and training for how to deal with that. Maybe grappling, maybe just how to hold a person off or provide a very basic defense against a contact weapon while deploying a defensive sidearm without shooting one's self in the hand/arm that is being used for physical defense.
My question for folks would be what is your plan for when someone charges you from 21 feet away but has no visible weapon? You can't just shoot them for running towards you. Pepper spray is probably a good option for many but I prefer to back it up with grappling skills.
I'm not a gun selling kinda guy (one of my many flaws) but I agree with the sentiment.
I am horrible at working out on my own. I like the motivation of someone trying to break my arm or strangle the life out of me instead. Really brings home a sense of urgency.
An important thing to remember, and I think I saw it posted earlier in this thread, is things like our own age and abilities.
We have to be realistic about what our options are. That is not to say we can't expand those options, though.
Very well said.