I'm torn on the gun ownership issue. Liverpool, I think that your car comparison is a little flawed as it is difficult to kill 32 people in the same way that this person has with a gun. Also, I would imagine that far more murders happen throughout the world with guns rather than cars.
I do know, however, that if the US govt. banned weapons of this kind that the criminals would still be able to get their hands on them on the black market. All it would do is make it harder for legitimate people to get them. The crims would still have access, granted it would be a little harder and certainly more expensive for them.
When Australia took the hard line on weapons I know it affected many people that I know who were responsible gun owners. My brother, for example, had to hand in some guns that he absolutely loved because they were banned. He used them for shooting wild pigs, foxes and rabbits on ours and friends farms. This was legitimate farm use. Not only did he have to hand them in but he lost a lot of money in having to do so on the cost of the guns.
Having said that, if it keeps these types of guns out of one more madman's hands then it is worth it. As I said, I am torn. I wish that they could come up with a way of only having them in responsible hands or an economically viable hand-in system. Unfortunately, I think that this is impossible.