A free society is also a vulnerable society.

This fact was chillingly demonstrated Monday on the campus of Virginia Polytechnic Institute when a disturbed 23-year-old, Cho Seung-Hui, who hated women and rich kids, went on a shooting rampage that left 32 innocent people dead.

College campuses are not supposed to be scenes of seismic, senseless violence. Neither are lawyers' offices, or restaurants, or Amish schools, or shopping malls. Americans are, for the most part, civilized. Our children grow up, for the most part, in safe havens. We gather together to learn, to worship, to play games, to work. We move freely about our business.

It is our civilized expectation that we will live through today and see tomorrow.

But then some wire in the human network gets crossed, and a deranged killer emerges. And little or nothing can be done to prevent the random attack.

Yes, there had been early danger signs with Cho, but no one was sufficiently alarmed -- or felt responsible enough, or empowered enough -- to intervene in his private life. And that is also characteristic of a free society. We leave people alone, in some cases too much. Isolation, loneliness and depression can backfire. Evil can take over.

Cho was an enigma. His classmates knew him as "the question mark kid." During introductions in an English class last year, he sat sullenly in the back of the room and refused to speak. On the sign-in sheet he put a question mark instead of his name. He wrote obscene and violent screenplays about stalking and killing and sexual molestation -- material so disturbing that he was referred to counseling by the English department.

"When we read Cho's plays, it was like something out of a nightmare. The plays had really twisted, macabre violence that used weapons I wouldn't have even thought of," a former classmate wrote in a blog. Students talked "with serious worry" about whether Cho could be a school shooter.

Sadly, they were right.

It is an unfortunate fact that a deranged madman intent on killing -- particularly one who is willing to die in the process -- has a free hand in a free society. And a school is a particularly target-rich environment, especially for one who doesn't care whether his victims have names or not.

The extent of the bloodbath may be directly proportional to the expectation of peaceful people that they will not be methodically murdered today.

Of course, people do respond intelligently, even heroically, as witnessed time and again, from the airline passengers who overwhelm a would-be bomber to the students at Virginia Tech, who continued to hold doors shut even after being wounded. But their heroism doesn't change the fact that the rules of freedom allow for the infiltration of madmen in the first place.

In response to Virginia Tech, the pro-gun crowd is touting more guns for self-defense. The anti-gunners blame the weapons. Politicians scramble to avoid the fallout. You can assign your own reasons for random violence from a full slate of sociological sicknesses.

But you will be hard-pressed to discover a cure. A random shooter is difficult to identify and even more difficult to intercept. No campus gun ban, such as the one proposed last year at the University of Utah, would have stopped Cho.

After several children were arbitrarily killed by a milkman at an Amish school in Pennsylvania last October, staunchly anti-gun Democratic Gov. Ed Rendell spoke the truth: "No proposed law, none that I would think of or none that I've seen, could have ruled out this situation. ... You can make all the changes you want, but you can never stop a random act of violence by someone intent on taking his own life."

It is simply an unpleasant fact that in a free and open society, such violence will take place. This is no comfort; it is merely true.

Though it is unlikely that you will ever face a madman or a terrorist, that unlikelihood doesn't change the fact that you are fundamentally vulnerable.

We all are. It is a condition shared by free people everywhere.

But our very vulnerability says something important about us. It signals that we are civilized, that we have values that transcend fear. It signals that we hold ideals that make the idea of a police state unthinkable. It shows that we celebrate human worth. We should keep that fact in view.

Our freedom to move, to gather, to live life as we choose, is a gift that tragic events must not be allowed to distort.

Today we can also grieve. We can lower our flags. We can pause for a moment to contemplate the terrible loss of life and promise. We can be united in feeling sick at heart. We can comfort those in mourning, and mourn with them.