Your question is a good one but I would look at it a different way
There is a hinge point with all weapons
Having a weapon in your home increases the chances of getting shot but knowing how to handle, store, clean, and care for a weapon makes these chances almost impossible
Same goes for carrying a weapon in public
If you are going to carry then you should practice using them religiously
If you are not 100% sure you can handle yourself and that weapon you should not have it around others because it is more of a liability then an asset
In the hands of someone that knows how, when, why, ect to use it a gun is a valuable tool capable of helping those in need.
As far as the percentage that carry that 'should' this is a tough one. I would guess maybe 10-15% of our population has the skillset to carry in public, this number includes LEO and military but thats just my guess.
Just to ask again then under a different premise. If someone you knew carried in public how would you feel around them, safer, not as safe, equally as safe as if they didn't have a weapon?