Would I have said, "We shouldn't be surprised"? No, because most of us are civilized and don't think of shooting people as a way to deal with our anger, hurt, rage, etc. Well, we might occasionally be so ticked off that we think something like, "If I had a gun, I'd pop'im one!" But we don't live there. We don't mean it. We don't plan for it. We don't do it. And we don't expect other people to do it, either.
But I do agree with Huck' that we don't need to look far for the reason, when such things happen. Oh, there will be analyses as to the shooter's mental state and/or motives, but we need to shoulder some responsibility for having allowed our society to slide further and further from any measure of reverence, of respect, for God's moral laws, one of which is, "Don't commit murder" (my paraphrase).
Still, the horror of these events shocks us to our core. The massacre of innocent children; the depth of grief experienced by the families and other loved ones of those who are killed, both children and adults; the awareness that first responders walk into scenes they will never, ever forget, though some will try in some unhealthy ways; these things and so much more bombard our minds even as members of the media bombard us with information, speculation, rumors, hearsay, occasional misinformation, and interviews, all in the name of bringing us the news. And we stay tuned, if we're able, because we crave more information, perhaps in the hope of hearing some one thing that will make all of the pieces fall into place, so that we can sit back, take a deep breath, and say, "Oh, okay. That's why. It's still horrid, but now I understand."
Many of us turn to God in the hope that He will make sense of it for us, but He already did that, long before He provided the means of our redemption through Christ Jesus, our Lord. And our hearts cry out, "Come, Lord Jesus!"