First ask the police why they need them, when they face no one but the same bad guys we have to deal with, *after* the fact. 

Ever consider that people experienced in dealing with violent threats and the tactics used to counter them might have more knowledge than you, Ever consider that what "the media" calls "assault weapons" are called "personal defense weapons" by DHS and other law enforcement agencies?

There are piles and piles of documented incidents of perpetrators not being stopped by single shots. Extrapolate this to include multiple perpetrators, factor in Sun Tzu's "rule of three", and the need for a standard-capacity magazine that holds 20-30 rounds becomes very evident. 

While hunting one can only use five-round magazines by law (except in game management districts that allow "varmint" hunting of prairie dogs, feral pigs, and the like), and the AR platform and others have been proven at taking game. Almost irrelevant however, as the 2A has nothing no to do with hunting.