This is first and foremost another tragedy, and terrible for the victims and those involved.
It's not a sad world we live in -- it's a sad USA (cue the "love it or leave it" crowd, but tell me that this, Las Vegas, etc., aren't sad). These kinds of mass shootings occur in one country in the developed world on a regular and almost predictable basis, and there are a ton of people who want to throw up their arms and say "this is just reality, too bad we can't do anything about it, 2nd amendment, blah blah blah" -- Ted Cruz's quote that we can't do anything about it "because people will just use the weaponry that is available to them" is the argument made by those who favor sensible restrictions on firearms. Some people will call those arguing for sensible restrictions on firearms hypocrites because they didn't call for sensible restrictions on renting trucks -- although restrictions do exist, and the use of vehicles to commit mass atrocities don't occur with regularity. Others demonize "liberal media" for suggesting that there is a way to sensibly restrict arms sales. The US president portrays it as a mental health issue months after lessening restrictions on the mentally ill being able to purchase firearms. Few people want to acknowledge a gun industry backed by the NRA that almost seems to encourage this. People want to lionize the person who shot back as an example of a "good guy with a gun," but ignore that the killing was already done by the time that happened (others still want to see more guns in churches). Others will say that "the liberals" want to take all of our guns away, when nobody arguing for sensible gun laws is making any such argument.
Counting the seconds until Cal comes along and uses the term "moron."