Well, what you easily dismiss (self defense) has been proved a need quite few times. I'm sure you can google as well as I can, but I can readily recall several instances where a single man repelled multiple home invaders because he was armed with a high capacity rifle.You didn't answer my question, and we've already established that the second amendment is not an absolute right.
If four guys kicked in your front door I guarantee you'd understand why no one in that situation has ever said 'no, that's too much ammunition'. And that applies to both rifles and handguns.
Heck, I can even show you an instance where a police officer got into a shootout with a suspect and hit him 22 times with his .40 service pistol and finished him off with his shotgun as they guy was still in the fight. One guy.