I mean, gun control is the obvious thing that comes to mind when someone says, "If Sandy Hook can't change things, nothing will." But I was also referring to our descent into this post-fact, conspiracy-addicted society. This was pre-Trump--conspiracy peddling hadn't yet taken complete hold as the primary platform of one of our major political parties---so this was our chance to say, "okay, 9/11 truthers were bad enough, but this is truly heinous" and categorically shun conspiracy theorists and those who profit off of them from our society. Instead, we tolerated them with no worse than an eye roll and soon learned that a quarter of the population truly wants to be lied to if it feeds their fear, distrust, and hate...more than enough to keep people like Alex Jones rich.
As always in human history, the message--and the truth--doesn't really matter. Whoever says it loudest, fastest, and most convincingly usually wins the day and plows over the majority of society, who are decent, adverse to confrontation, and put a lot of faith in decorum and others' ability to feel shame.
In the past, you at least had to earn your platform, so that did an okay job of keeping the reach of the true sociopaths contained. Not no more.