"They're lightweight, relatively cheap and extremely lethal, inspired by Nazi infantrymen on the Eastern Front during World War II. They're so user-friendly some retailers recommend them for children, yet their design is so aggressive one marketer compared them to carrying a "man card"—although ladies who dare can get theirs in pink. And if the last few mass shootings are any indication, guns modeled after the AR-15 assault rifle—arguably the most popular, most enduring and most profitable firearm in the U.S. -- have become the weapon of choice for unstable, homicidal men who want to kill a lot of people very, very quickly."