Your chart doesn't have the Y axis detailed, what does it represent?
http://www.project.org/images/graphs/Firearms-Crime.jpg
Here is a chart with general gun crime factored in. If anything, guns have been a continuous problem (vastly increased through the war on drugs stages, to be fair).
I don't think many people 'suddenly' think guns are a problem, rather the non-stop media and availability of said information makes people more fixated on the issue than before, yet the position most likely still existed prior.. just a thought.