The need? Simple. The 2nd Amendment wasn't meant for hunting or home defense, it was a defense against tyranny, and allowed a culture that prevented something like Egypt or Libya from being necesary here in the US. There is no reason to stop the proud tradition.

In addition, many 'assault rifles', which really is just a name for guns that have 2 of a certain amount of cosmetic or comfort features, CAN be quite useful for home defense, hunting, or general sporting. What is your NEED for a home defense shotgun? What does buckshot do within 20 yards that 2 quick shots from a 5.56 or 7.62x39 wont accomplish? Especially with the newer tailor made defense and hunting rounds for them.

Also, explain to me how a gun with the following is more dangerous than say, a 12gauge semi with buckshot.
AR-15 with collapsing stock, flash hider/threaded barrel, detachable magazine, pistol grip, and bayonet lug.

That AR is a quintessential assault weapon. Only attribute it's missing is a grenade launcher (And do note, we're talking the type such as the m59/66 Yugo SKS has, not an M203 which qualifies as it's own weapon, and doesn't count towards the AWB parts.)

That collapsing stock will allow a shorter person to be comfortable shouldering it, as opposed to one set length off the bat. That flash suppressor or threaded barrel wont make one bit of difference either way whether you're using it for crime, or for legal activities. Detachable mag? Why the heck not. It's a simple feature that most weapons now have for convenience. Pistol grip also allows a more comfortable and ergonomic grip. The bayonet lug? It lets me put a pointy piece of metal on the end. Utterly useless for almost any activity legal or otherwise outside of a warzone. But for purists that like their weapons to look authentic, the lack of it is just a big glaring FU from the government.

My personal need for it is nil I'll add. However just because I don't NEED it, doesn't mean no one does. In addition, can you tell me how that iHop massacre would have been any less deadly if he had a pump action shotgun with an extended tube? Any pistol with a double stack magazine? A 'sporting' rifle that is semi auto, like say the FNAR?

Remember, different strokes for different folks. You might be comfortable with your shotgun and PX4 or G23. I'm comfortable with my CZ83 and my Benelli Supernova. Some people prefer rifles over shotguns though, and why tell them that because their rifle of choice, one developed with CQB in mind at that, is inferior or useless and they don't need it, would be rather insulting to them, and is shortsighted IMO.