In my opinion this discussion goes the wrong way.
The question should never be, why you need something. It should be, why something has to be banned. And if there are not damned good reasons to ban something, it must not be banned.
If you jump on the "I need this for X"-train, you'll end up, as we did in Germany. Every time I want to but a gun, I have to proof, that I need it (for example fot target shooting). That's a pretty simple way, to limit the number and type of guns. Especially if you only accept a limited number of things people need a gun for (for example self defense is usually not accepted over here).
Gun laws are like traffic laws. It makes perfect sense, to ban people from drunken driving and require them to stop at a red traffic light. But it does nothing good to require people to explain the need for every vehicle they own.