Simply another symptom of human beings' overall inability to accurately determine relevance and causation. This often results in overreaction in ways which are ridiculous and nonsensical, and underreaction in ways which are more relevant and useful.
In the case of gun violence and mass shootings, it results in silliness like this, instead of a rational, reasonsed, and honest approach to understanding and mitigating the factors which actually result in gun violence. Of course, our style of public discourse which seems to primarily be based on rhetoric, paranoia, and mindless reactiveness, doesn't really lend itself to productive discussion and solutions.