Understandably, the National Review didn't want to be associated with the writer of such an article (even though the article appeared in another online magazine) and of course any publication has the right to make that choice. However, I cannot help but feel that this isn't really the correct response to a controversial--even offensive--bit of speech.
The problem with simply denouncing the piece as racist and punishing the writer--who, it should be noted, has previously provided a diversity of opinions on the National Review's pages over the years, differing from the majority of the magazine's writers on issues such as war and religion--is that it does not serve to debunk the actual piece that was so offensive in the first place. Someone who would actually agree with what Derbyshire wrote would simply see this as an unpopular opinion being silenced--as in "see, Derb was willing to state an unpleasant truth and the P.C. brigade couldn't handle it!"
Better would have been to challenge the statements in the article itself, perhaps publishing a rebuttal. The rebuttal can address the shortfalls of stereotyping, of mistaken assumptions based on race, and of course the awful example it would set for children to teach them to fear and avoid those that are different. The rebuttal can suggest that a better lesson for children is that while they should always keep their wits about them and avoid becoming an easy target for violent crime, it would be a shame to live in fear and mistrust. It can even state that on average, they have a better chance of becoming a victim of a crime caused by someone of the same race than by someone of another race.