This article is important because it shows the unintended consequences of network filtering.<p>However, the author veers into conspiratard territory when he regurgitates the right-wing victim-hood trope:<p><i>Andrew has discovered the issue I write about in my new book, “God Less America.” Public schools have become leftwing indoctrination centers.</i><p>This statement is unfounded. I'm sure plenty of lefty, libertarian or non-Republican websites fall under the "political/advocacy group" category. I imagine PETA, LEAP (Law Enforcement Against Prohibition), Democrat campaign web sites, etc would be banned. A dozen right-wing web sites on a ban list containing thousands of entries is not statistically significant. Only a proper analysis can show an actual, demonstrable bias.