However it is the business of government, as far as Christians are concerned, to punish evil. As 1 Peter 2:14 says that governors are "sent by [God] to punish those who do evil and to praise those who do good." Or as Romans 13:4 says of rulers, "But if you do wrong, be afraid, for he does not bear the sword in vain. For he is the servant of God, an avenger who carries out God’s wrath on the wrongdoer." A good government, whether secular or religious in nature, has a duty under God to make moral decisions and, insofar as it has power, to use the sword to enforce those moral decisions.
So it follows that governments have the right and duty, as they are able, to censor pornography. Whether they in fact do have the power (or even the willpower) to do this is another question. The sword that God has given to them may not reach quite as far as our internet connections, and some in a parliamentary democracy would see advantage in making sure that the sword remains short.
This is not a question that I've spent a lot of time thinking about, but I started thinking about it again because of the proposal currently before our local council to have a brothel built just round the corner from us. The particular question that has started to interest me is the link between pornography and prostitution (and perhaps further, the link between prostitution and human trafficking). Al Mohler's blog had an article about this subject in August 2005, where he mentions the work of Pamela Paul. And I also come across this quote in a 2006 article
The more often men purchased sex, the more they were to view sex as a commodity, and the more often they were to hold false information about prostitutes: most freely choose prostitution, they enjoy their work, they make lots of money, etc. Hughes suggested that if an education campaign debunked such beliefs and gave these men a more realistic view of the life of prostitution, they might be willing to change their behavior.25
Recently commentators in the United States have noted that pornography is becoming more culturally acceptable at the same time that it is becoming more violent and degrading toward women. This problem must be addressed in order to eliminate the demand for sexual trafficking, since researchers have found a link between pornography and prostitution, with men who solicit sex acts to be twice as likely to have viewed pornography as US men in general.
The same article reminds its readers that "Up to 800,000 people are trafficked internationally each year for sexual exploitation and forced labor, 80% of them women or girls."
I might do a bit more digging around on this subject. I found a pdf file of a 2004 article by Dr. Donna Hughes, Best Practices to Address the Demand Side of Sex Trafficking, you can download it here and it makes worthwhile reading.