I think the reason is publicity. It's what we see and hear all the time. There are constant news stories of abducted kids, for instance. Now, it's true that only 1 in 1000 kids who was abducted or harmed was harmed by a stranger and not a family member, but people these days are so afraid of a stranger abducting their child that they don't let children play in the yard by themselves. The chances of children being involved in school shootings are exceptionally rare, in the one in millions range, and yet we hear enough about them that companies actually make (and sell) bullet proof backpacks, and mothers who show up at school when called are arrested.
We don't hear about the millions of children who played outside safely every day, or the millions who went to school without incident, or the millions of parents who showed up at school for legitimate reasons and didn't then try to murder everyone in sight.
And it's not just the news media. It's shows like Law and Order and it's incarnations, and NCIS, and CSI, etc. etc., that are constantly showing us bad things happening to people.
We're exposed to it now. When I was a kid, most people wouldn't have really known the word "psychopath." Now it's everyday vocabulary.
Awareness of these things is commonplace, and as we get more nationwide news we hear more of the rare cases, and it makes it seem like the risks have increased, whether they actually have or not.
For what it's worth, I complain constantly about the unsafe drivers (can we say three people running the red at ONE light yesterday while I was already in the intersection, the last of whom was reading a stack of papers while he was driving?) and the fact that people seem to be too selfish to not run red lights or put away the cell phones (I see so many texters driving beside me), etc. I dread Google Glass becoming commonplace and seriously consider moving to a place with good public transportation if it isn't outlawed while driving.