If we lose gun rights - it will because of incidents like these and not conspiratorial plots.
Two thing can drive legislation:
1. An emotional response overwhelming the positive use of firearms.
2. An availability cascade (meaning that all folks will remember are the negatives - esp. since the positives are not played up that much).
Given similar incidents like Martin, the new one in Florida with the kids and loud music vs the not found shotgun, guys pulling guns over punches in line on Black Friday and the like - the public will have in their mind the memories of irresponsible gun owners. Even though responsible far outweighs that. Folks remember the emotional vivid incident and overestimate its probability.
While the legal mandate for gun education is something we debate, I still think that if you are serious about SD you need to be educated on more than punching holes at the square range. Sure, some can't afford it, etc. But it's a good idea.