I agree 1000%
I think everyone should do as they wish and carry as many rounds as they can possible carry. But I have trouble seeing any circumstance within the realm of reasonable possibility where you're going to need more than a few rounds.
If you're running out to your vehicle to get more ammo it means you've disengaged from the immediate situation and are planning on returning to the fight, which negates your argument of "self-defense". Also you're assumedly returning to a situation where there's going to be a police response and the last thing they'd probably want is another unknown person wandering around with a weapon while they're looking for a bad guy.
Why do you need all of this unless you are going around looking for trouble