“Opponents note that the powers given the government under the bill are very broad. Because the bill targets domain names and not specific materials, an entire Web site can be shut down. So for example, if the US determines that there are copyright-infringing materials on YouTube, it could theoretically block access to all of YouTube, whether or not particular material being accessed infringes copyright.
Free speech advocates argue that Internet censorship laws are inevitably used for purposes other than the ones claimed by lawmakers.
For instance, Australia in recent years set up a “firewall” around its Internet, with the intention of blacklisting child pornography Web sites. But a list of the blocked sites, leaked to Wikileaks, showed that the Australian government was censoring more than porn: The blacklist contained religious and political Web sites.”