in reality, you really don't need 15...20....30 round clips/mags for self defense (especially if you consider the avg household probably keeps additional clips around). once you start firing you are more than likely to scare someone off to begin with.
100rd drum magazine is really bizarre for anything outside of a combat op where you need sustained firepower and less reloading. typically you see 100-200 round ammo boxes/drums on a squad support weapon like a m240/249, so you know that really makes you wonder what civilian use they have (is there going to be a support gunner helping you to defend your home, lol)
however...at what point are these laws interfering with people's rights. we as a country generally don't like being told what to do, yet we have legislators constantly doing so. Banning sugary drinks, telling us what we can and can not do in our cars, and so forth.