[1] http://articles.cnn.com/2008-02-19/tech/satellite.shootdown_...
http://www.chinadaily.com.cn/world/2010-07/19/content_101211...
The stated reason is not terribly compelling. Deorbiting satellites are very small, the Earth is very large. As the article correct points out, nobody has ever been injured by space debris, or even killed. Dozens of people are killed by cars every day, yet each automobile fatality does not make it into the New York Times.
Note the timeline of the two ASAT tests. China shoots down a satellite in January. One month later, the United States does the same thing, presumably in response. Why are the Chinese shooting down satellites?
A critically important piece of context is that China really, really hates satellite-guided bombs, such as the American JDAM. This is because the Chinese embassy in Belgrade was hit by five JDAMs during the 1999 NATO operation in Yugoslavia, killing three people, and injuring twenty others.[1]
The American position is that this was a simple mistake in targeting, as they were attempting to strike a Yugoslavian arms warehouse 180 metres away. The Chinese maintain the Bill Clinton personally ordered the attack, possibly while drinking the blood of Chinese infants, as a part of his mad genocidal urge to destroy the entire Chinese race. (The reaction of the Chinese media to the bombing was remarkably hysterical; it's essentially their 9/11, only they didn't have the option of invading the US)
Various cynical independents have pointed out that, five weeks earlier, the Yugoslavians had actually managed to shoot down a F-117, the only combat loss ever sustained by a stealth aircraft, and that the Chinese had been seen buying recovered debris from locals. You could make an amazing jump in deduction here, and conclude that they had been storing debris in their embassy, in the hopes that the Americans wouldn't bomb it in retaliation.
The JDAM depends on GPS satellites, which have to be in a fairly low orbit, for accuracy, and so that the receivers can use small antennas; where they are fairly vulnerable to ASAT missiles. (I don't believe any current ground-based ASAT missiles can hit targets in geosynchronous orbit, which is 15,000 kilometres higher than MEO. This is an educated guess, not a certainty: governments are chary about giving out details on the performance envelope of missiles.)
An ASAT weapon isn't something you want to use at the drop of a hat. Blowing something up in orbit produces a lot of debris, most of which hangs out in space for years. There's various doomsday scenarios, of varying plausibility, where blowing up a satellite produces high-velocity shrapnel which destroys other satellites, which in turn fragment, producing a cascade of destruction, throwing us back into the stone age.
In conclusion, you can blow it up, but you probably don't want to.
1: http://en.wikipedia.org/wiki/U.S._bombing_of_the_Chinese_emb...