In order to support the conviction that censorship is needed, one must be able to show how the information in question - that which is to be censored - does harm by imposing upon the rights of others.
This is why it's so often so difficult to rationally support censorship: the sharing of information is very rarely something that imposes on other people's rights. Sharing personal information without permission, libel, hate speech, and slander are illegal because they can be shown to violate the rights of others. But does pornography do this?
Absolutely not.
Those who work in the porn industry are volunteers, working for legal, taxed pay, be they on or off screen. Those who pay for the pornography are interested in seeing it, because they enjoy it, and as adults, they are totally free to do so. In fact, they have a right to do so, and censoring pornography would violate that right.
It needs to be understood that the Internet is a worldwide endeavor, not owned by any particular country. Thus, it can not be controlled by any particular country. A nation can, to an extent, control what websites are viewed and produced by its people, and some communist nations, like China, try very hard to do this. Censorship is never done perfectly, though, and is often done shoddily, so that it merely wastes resources, rather than attaining the mass ignorance it aims for.
People are very good at getting what they want, despite censorship. If pornography were to be censored or banned by the United States government for its population - something I can guarantee will never happen without the total dissolution of freedom and democracy - people would still manage to get it when they wanted it. They might build uncensored mini-networks of computers or, more likely, they would simply buy porno in print.
Printed pornography is, by the way, another thing that the prudes of the world have tried to ban from free trade, and they have failed. Freedom of expression is freedom of expression, and if it can't be shown to do harm, it can't rightfully be stopped.
Those who are against pornography - usually monotheistic religious people who are self-centered enough to feel justified in imposing their personal preferences on the disinterested - have tried to draw causative lines between pornorgraphy and the degredation of society, much as they've tried to draw similar lines between homosexuality and the end of culture as we know it.
It seem the religious just can't stand the thought of someone else having the fun they're not allowed to have - especially since fun is something they're often not allowed to have at all if they want to please their gods. And so, they make up stories with the intent of crashing the party for everyone else.
The extroardinary claims of the porno-party crashers are equally unsupported and equally fabricated, though some are sillier than others. Prudes claim that pornography leads to violence, sexism, murder, and even alienation from one's own family. It causes children to look to porn stars for love and attention. It causes men to forget their wives. It causes women to be degrated, and encourages violence upon them.
None of these claims can be supported with sufficient empirical evidence or with reasoned argumentation. While porn addiction can happen, so can food addiction, caffiene addiction, internet addiction, and in feeble old ladies, housecat addiction. That people can get addicted to these things is not reason enough to ban them. People can become addicted to anything: all it takes is positive neurochemical reinforcement associated with a particular behavior, and the absence of anything better to do.
Some forms of porn are distasteful, yes, but so are other forms of art. Films like "Expelled: No Intelligence Allowed" and "Pink Flamingoes" are garbage, just as a crudely filmed, violent snuff film might be garbage, but that doesn't mean they can be rightly banned or censored. It's important to recognize that if we want the freedom to express our own points of view and make our own art, we must accept that the same is true others, even if we deeply disagree with what they say and do.
Those who are so deeply terrified of pornography should, instead of pushing for censorship, argue publicly against viwership. They should take a stand against choosing to watch porn by arguing that porn is harmful and by showing it to be harmful, and in order to get to the people who need their message the most, they should speak in the nude.