That's an understandable point of view, but the ease of acquiring an assault rifle isn't going to deter someone, compared to someone making an IED. Mental cases will always exist. But what it has done, is brought bigger issues to light. Depends if you still believe this is just about one mental kid and a school, or if it's about the ease of which a massacre could occur.
So with that, I go back to saying I'll go to a class to keep my guns or more intense background checks (using this as an example for possibly deterents). I do it for my job due to where I work (which also intensifies my belief in gun ownership) so I don't have a problem doing so every so often. A massacre can occur too if that same kid got in a semi and drove it down a crowded sidewalk. Opportunities are all around for this kind of person which they would take advantage of.