The counterintuitive claim that the Internet causes us to become more extremist and close-minded, rather than exposing us to a haphazardly unbiased array of unexpected viewpoints, is the cornerstone of this challenging and dense book. University of Chicago legal scholar Sunstein (Democracy and the Problem of Free Speech) contends that we are witnessing a decline in the influence of ""general interest intermediaries"" and an increase in highly specialized forums for information Web sites that allow us to ""personalize"" the news, customized cable TV channels devoted only to fashion, music, sports or other specialized subjects. In such a culture, he argues, we have the seductive ability to see only what already interests us and to filter out any exposure to the different concerns and political opinions of fellow citizens, inadvertently robbing ourselves of a truly democratic conversation. Sunstein posits that the solution to this self-imposed intellectual isolation lies in the seemingly unpalatable but potentially workable realm of government regulation creating cyberspace ""town halls,"" requiring political Web sites to provide links to groups with opposing views. Sunstein's critics will counter that most mainstream media outlets, owned by an increasingly small number of corporate conglomerates, don't provide their audience with a diverse range of programming in the first place. But this will not stop them from finding Sunstein's arguments complex and thoughtful. (Mar.) Forecast: This slim, sleek volume perfectly designed to appeal to Internet-era attention spans will attract browsers, while Sunstein's controversial claims and a national tour will likely garner him some media attention.