Society needs fewer massacres
Those of us who are in favor of banning assault rifles and large magazines are seeking to balance the needs of society with the needs of individuals. Striking that balance, properly, is how freedom is supposed to work in the USA. The pursuit of your happiness can't just trample my pursuit of happiness.
For the individuals who like them, military rifles designed for combat and big clips may be fun things to use and possess. But civilians don’t need them for hunting or protection. There are plenty of reasonable options that will fill those needs.
Whereas, society needs fewer massacres.
So, you say you need an assault rifle to fight the government or an invasion of zombies? Like, you're stocking up provisions for your bunker, to be ready for the day you need to go Rambo?
Rather than needing military weaponry, you need better taste in movies.