Catholics and gun control

The shootings in Connecticut have affected the country more deeply than any event since the attacks of 9/11, in my opinion.  They represent an evil that cannot be remedied by any legislation, though legislation may play a role in making such events less common.  I do not want to diminish the horror of last Friday's events by framing our response in strictly legal terms, but we are a Catholic legal theory blog, and the legal debates are now upon us.

I am not a gun owner, and I have never quite gotten my mind around the full-throated defense of gun rights.  (I understand the Second Amendment argument; I'm referring to the various forms of the "any limitation on gun ownership is bad public policy" argument.)  In my view, the NRA has a similar function to NARAL in that both groups make reasoned discourse on the underlying issue more difficult.  I don't believe that there is a "Catholic" position on gun rights, but I do believe that there is a Catholic understanding of freedom that is in considerable tension with the understanding of freedom that seems to animate the arguments of some gun rights advocates.

So here's my question: Why should a Catholic who takes seriously our obligation to cultivate the common good oppose a ban on the sale of assault weapons?  I'll assume the elusiveness of an agreeable "assault weapon" definition -- I understand that's an obstacle, but that does not seem to be the only sort of objection.  I'm interested in the more principled grounds for opposition.  I ask this question in a fully non-snarky way -- I'm not an expert on guns or gun laws, so I would like to be pointed to the best arguments why a Catholic worldview is consistent with the private ownership of guns designed for killing at a high rate of speed.