As a baby reporter in Texas, I covered what we euphemistically called mental health services in the state. These “services,” reserved for the dangerously ill, involved brief, groggy hospital stays followed up with a handshake, a script for enough pills to stun a moose and all best wishes: See you soon!

Unless something worse happened, the patients were bound to be back. And just as surely, whenever I’d return to the newsroom after a trip to one of the state-run mental hospitals, my editor could be counted on to joke, “You didn’t catch anything while you were there, did you?” Schizophrenia cooties, I guess he meant, or bipolar bugs.

The national conversation since last week’s shootings at Sandy Hook Elementary School in Newtown, Conn., has reminded me of that guy, whose fear of mental illness may or may not have been treatable. And our still under-informed, over-anxious understanding of mental illness — or of any cognitive or neurological difference, for that matter — suggests that we haven’t come very far in the decades since he snickered about depression being contagious.

The shooter was “known to suffer from Asperger’s syndrome,” cable anchors tell us, as if that might explain a child-killing spree. But there is no link — none — between violence and this high-functioning form of autism.

And though you might not know it from some of the coverage, Asperger’s isn’t a mental illness at all, it’s a developmental disorder. The young adults I know with Asperger’s are all smart and sweet, and simply had to work harder to learn the social cues that came effortlessly to their peers. When one of them got into a top college a few years ago, his mom fantasized about sharing the news with every kid who was ever mean to him in middle school: “Have fun at DeVry!” Because young people with Asperger’s are far more likely to be bullied than to do any bullying.

I’m equally chary of vague reports that the shooter, Adam Lanza, “had some kind of personality disorder” and was “on some kind of medication.”

Maybe he did and was, but there is no medication that treats Asperger’s itself, and fears that antidepressants can set off killing sprees are mistaken: “There’s no evidence to support that,” said Bernard Vittone, director of the National Center for the Treatment of Phobias, Anxiety and Depression. “Even the evidence linking it to suicide in children and young people is shaky, and I don’t know of any evidence linking violence in general to antidepressants.”

Some of our other most beloved biases have come out to play in the days since Lanza opened fire: How quick we are to blame the slain mother of the kid gone horribly wrong. If you’ve had to sleep by your friendless grown son’s door, to be there to calm his fears, then go ahead and judge Nancy Lanza’s decision to take her son to a shooting range in a desperate attempt to connect with him.

Somehow, in painful moments like this, even what we do know seems to slip away from us — so we perpetually wonder how such a thing could have happened in a community one and all regarded as safe, as if being “close knit” or “low crime” had anything to do with it.