When teenage thugs are called "troubled youth" by people on the political left, that tells us more about the mindset of the left than about these young hoodlums.
Seldom is there a speck of evidence that the thugs are troubled, and often there is ample evidence that they are in fact enjoying themselves, as they create trouble and dangers for others.
Why then the built-in excuse, when juvenile hoodlums are called "troubled youth" and mass murderers are just assumed to be "insane"?
At least as far back as the 18th century, the left has struggled to avoid facing the plain fact of evil -- that some people simply choose to do things that they know to be wrong when they do them. Every kind of excuse, from poverty to an unhappy childhood, is used by the left to explain and excuse evil.
All the people who have come out of poverty or unhappy childhoods, or both, and become decent and productive human beings, are ignored. So are the evils committed by people raised in wealth and privilege, including kings, conquerors and slave owners.
Why has evil been such a hard concept for many on the left to accept? The basic agenda of the left is to change external conditions. But what if the problem is internal? What if the real problem is the cussedness of human beings?
Rousseau denied this in the 18th century, and the left has been denying it ever since. Why? Self-preservation.
If the things that the left wants to control -- institutions and government policy -- are not the most important factors in the world's problems, then what role is there for the left?
What if it is things like the family, the culture and the traditions that make a more positive difference than the bright new government "solutions" that the left is constantly coming up with? What if seeking "the root causes of crime" is not nearly as effective as locking up criminals? The hard facts show that the murder rate was going down for decades under the old traditional practices so disdained by the left intelligentsia, before the bright new ideas of the left went into effect in the 1960s -- after which crime and violence skyrocketed.
What happened when old-fashioned ideas about sex were replaced in the 1960s by the bright new ideas of the left that were introduced into the schools as "sex education" that was supposed to reduce teenage pregnancy and sexually transmitted diseases?
Both teenage pregnancy and sexually transmitted diseases had been going down for years. But that trend suddenly reversed in the 1960s and hit new highs.
One of the oldest and most dogmatic of the crusades of the left has been disarmament, both of individuals and of nations. Again, the focus of the left has been on the externals -- the weapons in this case.
If weapons were the problem, then gun control laws at home and international disarmament agreements abroad might be the answer. But if evil people who care no more for laws or treaties than they do for other people's lives are the problem, then disarmament means making decent, law-abiding people more vulnerable to evil people.
Since belief in disarmament has been a major feature of the left since the 18th century, in countries around the world, you might think that by now there would be lots of evidence to substantiate their beliefs.
But evidence on whether gun control laws actually reduce crime rates in general, or murder rates in particular, is seldom mentioned by gun control advocates. It is just assumed in passing that of course tighter gun control laws will reduce murders.
But the hard facts do not back up that assumption. That is why it is the critics of gun control who rely heavily on empirical evidence, as in books like "More Guns, Less Crime" by John Lott and "Guns and Violence" by Joyce Lee Malcolm.
National disarmament has an even worse record. Both Britain and America neglected their military forces between the two world wars, while Germany and Japan armed to the teeth. Many British and American soldiers paid with their lives for their countries' initially inadequate military equipment in World War II.
But what are mere facts compared to the heady vision of the left?
Thomas Sowell is a senior fellow at the Hoover Institution, Stanford University.