I don't like Internet filters, and not just because many folks can't read my blog (thanks, Mark!).
I don't like them because they impede political awareness (see, e.g., Andy Carvin's fantastic post on this).
I don't like them because in order to exercise one's right to free speech one also must have access to speech:
[T]he Constitution protects the right to receive information and ideas. This right is an inherent corollary of the rights of free speech and press that are explicitly guaranteed by the Constitution. . . . The dissemination of ideas can accomplish nothing if otherwise willing addressees are not free to receive and consider them. It would be a barren marketplace of ideas that had only sellers and no buyers. . . . More importantly, the right to receive ideas is a necessary predicate to the recipient's meaningful exercise of his own rights of speech, press, and political freedom. [Board of Education, Island Trees Union Free School Dist. v. Pico, 457 U.S. 853 (1982)]
And I don't like them because of the message they send to students: in an information economy, we don't trust you with information.