Skimming, while possible to do correctly, more often than not is not. As an article in the Washington Post explains, skimming is the prime symptom of aliteracy, an increasingly commonplace malady in the United States. This problem is serious - people who do not fully grasp what they read are likely to base decisions on opinions they once had, and will likely always have. According to Mark Twain, "The man who does not read good books has no advantage over the man who cannot read them."
While illiteracy is relatively easy to detect, aliteracy is much harder to identify. The distinction that may allow students to resist aliteracy is between efferent and aesthetic reading. Efferent, meaning for the purpose of absorbing information, and aesthetic, meaning purely for the pleasure of reading. Teachers need to emphasize aesthetic reading more.