Let me start off by defining an assault weapon. An assault rifle is a semi-automatic (Semi-Automatic means that you pull the trigger once, one bullet fires) rifle with certain military characteristics, while a machine gun (Banned in the USA) is a fully automatic rifle. The AR can fire around 60 bullets a minute for a skilled operator. The M4A1 is a machine gun used by our military. It can fire over 1,000 bullets a minute.
Assault weapons function essentially the same as a bolt-action rifle. If I own an MP 15 22 the rifle will function essentially the same as if I own a single shot 22 rifle, because if I pull the trigger one time, one bullet will fire. The difference is that the MP has a collapsible stock, flash suppressor, and a pistol grip, and therefore Senator Feinstein, Harry Reid, Barack Obama, Joe Biden and many others think you should not be able to own that gun.
Now I get to the question of why we need Assault Weapons. First off, it should not be a matter of why I need it, only that I can have it. The constitution states that I have the uninfringable right to bear arms. Taking away a semi-automatic rifle infringes upon that right. Theoretically, any politician who votes to take away these guns could be prosecuted, because they take an oath to uphold the constitution.
One reason is that semi-automatic rifles are just fun to shoot. Second, other than a shotgun, they are the best weapon to fight off burglars and home invaders. Third, the MP and several other rifles can be used for hunting.
In conclusion, it is not a question of “do I need an assault weapon”, it is a statement that “I have a right to an assault weapon.”