So far, I have seen the Virginia Tech murders blamed, in varying measures, on:
the lack of gun control;
and, by far the worst,
Of course I understand that it's a natural and valuable human trait to connect individual events to larger themes. But let me just say that much of what I've read so far (though not all) is not the result of considered reflection, but an unseemly eagerness to trot out whatever explanation most expeditiously confirms the writer's worldview.
Intellectual rigor has also been one of the casualties of this tragedy, I'm afraid.