Last week, my oldest brother was turned down again for parole. He has been in prison for almost 29 years since pleading guilty to first-degree murder.

His son - a nephew who was raised like a brother to me - will be in prison for the next quarter of a century. He accidentally shot and killed a friend during an armed robbery. He and that friend were attempting to rob a drug dealer.

Many years ago, a young man I mentored shot and killed a police officer.

I've known others who have killed or attempted to kill someone.

The wisest thing I can say about what ultimately motivated each of them is this: I don't know.

That's pretty much where I am about the "Arizona massacre" that left six people dead including a federal judge and 14 wounded, including a U.S. congresswoman.

I don't know what convinced the shooter to legally purchase a Glock and unload that devastating weapon into a crowd of strangers, which included a 9-year-old girl who was getting an up-close and personal look at democracy in action. She was murdered, too.

No one knows what led to that decision. And we likely will never know. The shooter, who reportedly had mental health struggles and other problems, probably can't explain why.

The easy answer is to blame it on our hyper-partisan political discourse, or on loose gun-possession laws, and pick whatever narrative best proves a point we've been wanting to make anyway, using this incident to express moral outrage.

Comparing it to the far-left '60s anti-government violence or the far-right environment into which Timothy McVeigh stepped into infamy in the mid-1990s might make me sound smart, contemplative even. Don't be fooled, though; I don't know.

Calls for a ramping down of hyper-partisan political rhetoric are in vogue because of the shooting.

A respectful tone, especially during heated, emotional debate, is always desirable.

Even soldiers have to be trained to override their conscience before they can kill.

One of the best ways to do that is to dehumanize the other side by asserting, time and again, that opponents are imminent threats to the republic and are Hitler-like and evil and need to be stopped at all costs, the kind of rhetoric that too often passes as debate today.

That needed to change, shooting or no shooting.

But responsible, passionate political participation is a bedrock democratic principle.

A lone gunman must not be allowed to change that.