Honestly? I'm going to burn plenty of bridges by saying this to anyone I know, but my reaction to this is "Meh. I don't care..." and it's taken me a while to get to the point where I can say that, but here it is.
Attachment is the key to all suffering. While, sure, I feel sympathy for the family and loved ones affected by this, the lives of the victims are over. They've continued with the next stage in the cycle of existence (heaven, limbo, reincarnation, etc.) and have nothing to fear, hate, etc.
The family members have every right to feel sorry and get upset; they're the ones who were attached to the victims. As a person, I can relate so I sympathize with them, but it ends there.
People going on and on about this are the ones asking things like, "How can anyone do this?" and that's also a form of attachment - ego and pride. Getting an idea that people are better than this, incapable of this and so on; painting an ideal picture of what humanity is and then becoming attached to that ideal. When something like this happens, it wounds their pride and deflates their ego a notch.
Remove yourself from that attachment and an incident like this is just another act by a person who was also suffering from the same pain caused by some form of attachment - jealousy, anger, rage, or whatever the emotion. In other words, there's no surprise that a person is capable of this.
If I have no ideal standards of behavior for humans that I've attached myself to, then I can't be upset by them not holding to those standards and an event like this become just another side effect of the suffering that already surrounds us.
I'll do everything I can to avoid causing people and animals anywhere to suffer on a large scale, but when an act like this occurs, obsessing about it is just wasted energy that can be used to continue to prevent suffering to others.