Why can't Homeland Security tell the difference between Al Quaeda and small children?

Schneier's op-ed for Salon explains why our "security" measures are taking away our liberties without foiling terrorists.
In the months and years after 9/11, the U.S. government has tried to address the problem by demanding (and largely receiving) more data. Over the New Year's weekend, for example, federal agents collected the names of 260,000 people staying in Las Vegas hotels. This broad vacuuming of data is expensive, and completely misses the point. The problem isn't obtaining data, it's deciding which data is worth analyzing and then interpreting it. So much data is collected that intelligence organizations can't possibly analyze it all. Deciding what to look at can be an impossible task, so substantial amounts of good intelligence go unread and unanalyzed. Data collection is easy; analysis is difficult.