I was thinking about it, and novelty / 'cool' factor aside, I can't come up with any valid, legal reason why a private individual would ever need one of these.
That said, it's a free country / world (well kinda), and people have the right to buy whatever they please, so long as they use it responsibly.
But with something as lethal as this, you know it's a disaster waiting to happen.
Just wait until some disgruntled college kid gets their hands on one and it'll make the likes of Columbine seem like a joke.
Like you say, very sinister Chris
Ciarán