There was a time when musicians could pull off a reaction song. "Ohio" by Crosby, Stills, Nash & Young is one such example, written in the aftermath of the Kent State shootings. But this was a product of a less globalized world in which information traveled at a speed that now looks as quick as the Pony Express. There were people who knew nothing about Kent State before hearing "Ohio." The last thing anybody needs is more awareness of what happened in Connecticut.
There will be a time when Sandy Hook will be fair game for song material, but only after it has been digested. Even then, most of these songs will suck. At least the context will be more interesting than a knee-jerk response of anger or pity. For now, it's off limits. Don't write a song about Sandy Hook. I'm not going to say please. Have some respect.