Did our angry political culturehelp motivate Jared Lee Loughner on what authorities say was his mad shootingspree? Maybe, but a more troubling question for me is why nobody stopped thisoften incoherent, irrational young man on hislong path to the rampagejust outside Tucson.

I don't just mean the people whosold Loughner his Glock 19 semiautomatic pistol in November, or the people at aWal-Mart who allegedly sold him ammunition a few hours before the assault. Imean the community in which he lived. This was a young man who showed signs ofmental illness, yet in our culture people couldn't or wouldn't stop him - evenwhen they knew his behavior was bizarre.

We leave people alone in America,to a fault. We walk past rambling, dazed homeless people every day, if we livein big cities, avoiding their gaze rather than seeking to intervene. And evenwhen we try to stop people whose behavior seems to pose a danger to themselvesor others, it's hard to do anything about it, as Loughner's professors at PimaCommunity College discovered.

Look at themoon-faced grin of thealleged shooter as he appeared in court for arraignment Monday. It's a hauntingphoto, not least because we have seen faces like that before - people who areseverely disturbed but on the streets in this era of"de-institutionalization."

Here's what I walked past theother morning before sitting down to write this column. Outside my subway stopwere two shopping carts, bearing what appeared to be the worldly possessions oftwo homeless people. They had fled on this bitterly cold day, but a distractedyoung woman in a thin jacket was walking aimlessly nearby, shivering. At atransit point, a ragged man with no teeth staggered out of the car. On anothertrain, a woman talked incessantly to herself, as if in a trance. Nobodyintervened. She didn't look suspicious; just crazy.

If you've ever worked in ahomeless shelter, you know that a substantial number of the residents havemental health issues, often combined with drug and alcohol problems. They mightonce have been in state asylums, out of sight and mostly out of mind. Thosewere nightmare places, and the de-institutionalization movement that put peopleon the streets was right, on balance. But the idea was to fund halfway housesand treatment, not just let people wander.

The Loughner case is telling inthat it shows how hard it is to do something about an unstable person, even ifyou try. Pima Community College said that Loughner last year "had fivecontacts with PCC police for classroom and library disruptions." Yet as Timothy Noah noted in Slate, hewasn't suspended until Sept. 29, after he denounced the college as "ascam" and his teachers as "illiterate."

Students and teachers knew thatLoughner was potentially dangerous. His algebra teacher, Ben McGahee, told ThePost that when he complained about Loughner's disruptions, "Theyjust said, 'Well, he hasn't taken any action to hurt anyone. He hasn't provokedanybody. He hasn't brought any weapons to class.' " Loughner "scaresme a bit," wrote one of the students in an e-mail quoted by The Post."Until he does something bad, you can't do anything about him," shewrote in a later message. "Needless to say, I sit by the door."

"His thoughts were unrelatedto anything in our world," his philosophy professor, Kent Slinker, saidin an interview with Slate's Christopher Beam. He was, Slinker said,"someone whose brains were scrambled." And yet he kept on rollingtoward the Safeway parking lot, buying his gun, buying his ammo, leaving behindcrazy YouTube videos that were advertisements of his madness.

The Tucson shootings haveprompted a national debate about the decline of civility in America. That'sgood, but we should expand the definition of "civil." A civil societyisn't just about less screaming on cable TV. It also has an ethic of community,so that people try, as best they can, to look out for one another.

There's a coarsening, uncivileffect when we watch homeless people ranting and mumbling, freezing in the cold- and cross the street, assuming that it's somebody else's business. It takessomething out of us, individually and as a country.

Like most of the problems thatmatter, Jared Loughner didn't sneak up on us and catch us by surprise. We sawhim coming and didn't do anything about it.