On Monday, Lieberman, who is chairman of the US Senate's Homeland Security and Governmental Affairs Committee, sent Google CEO Eric Schmidt a letter saying YouTube was unwittingly enabling terrorist organizations to promote violence against the US.

The letter, the full text of which is posted here, said that though YouTube has community policies regarding the content of its videos, but that "it does not appear that the company is enforcing these guidelines to the extent they would apply to this content."

The letter says videos identified by Lieberman's office include violations of those guidelines such as hate speech, violence and weapons training.

Lieberman also suggests that the removal of these videos "should be a straightforward task since so many of the Islamist terrorist organizations brand their material with logos or icons identifying their provenance."

In a quickly-posted response on its blog, Google said that it had reviewed and removed several of the videos flagged by Lieberman's staff, "primarily because they depicted gratuitous violence, advocated violence, or used hate speech." Many of the videos, however, Google declined to remove because they did not violate the YouTube community guidelines.

Regarding its refusal to remove certain videos, Google brought up the value of YouTube as an archive of diverse viewpoints, and as a venue for discourse.

"While we respect and understand his views, YouTube encourages free speech and defends everyone's right to express unpopular points of view," said the blog entry. "We believe that YouTube is a richer and more relevant platform for users precisely because it hosts a diverse range of views, and rather than stifle debate we allow our users to view all acceptable content and make up their own minds."

The discussion between Google and Lieberman extends a long-running legal debate regarding the responsibility of sites that host user-generated material to police the content of that material.

According to section 230 of the US Communications Decency Act, web hosts are entitled to restrict access to content they consider objectionable, but are not legally held accountable for failing to limit access. The ruling has much to do with the damage that could be done to the business of a site like YouTube if it were required to review every one of the "hundreds of thousands" (according to Monday's blog post) of videos posted to the site every day.

The involvement of a notable US senator on the other side of that debate, however, could mean that debate will be raised about how suitable the content of the Communications Decency Act is. Certainly, perceived threats to homeland security have been the impetus for changes to US law in recent years.

According to reports, Lieberman found Google's response to his letter to be "unsatisfactory," and there is some speculation that he may be seeking the means to more forcefully encourage Google to police YouTube content by way of legislation.