After giving this some thought, I'm moving more towards the "something must be done" side, but maybe not what a lot of you Euro-weenies think must be done. I am reminded of a meme seen recently, "How many more killings are needed before you give up your guns?", with the response being "How many more rapes are needed before you cut off your dick?" I think this sums up the views of many Americans, enough to ensure a gun ban will never happen.
So... what, then? I am also reminded of something a nameless Euro-weenie said years ago on some forum somewhere that stuck with me. "Your typical American kid will have seen 1000 murders on TV before they're 10 years old, but not a single tit", which I think strikes at the heart of the peculiar nature of puritanical America. Years later, an American child of 10 will have *committed* thousands of murders in increasingly realistic video games.
I don't think it's a coincidence that the particular type of mass murderer we're talking about is usually in their teens or twenties.