I am going to attack this from a different angle and go after the somewhat understated underlying assumption that censorship is ethically, morally or legally wrong.
Legally, the U.S. government is forbidden from taking actions of censorship. However even that has exceptions.
http://en.wikipedia.org/wiki/United_States_free_speech_exceptions
Ethically, if I disagree with you, I am under no ethical obligation to spend my time, effort, or other resources spreading your message. If the power disparity between us is great enough however it can still censorship.
Morally, well this is a more tricky one because I have never found a moral that wasn't harder to nail down than water flowing over a Teflon pane in zero g. As far as I can see saying something is moral is no more then saying that it is something you personally and/or society (by any definition of society) agrees with. Pick any 100 people at random and you'll have a fairly unique set of "morals". Ethics at least has the obligation of defining central principles and justifying the generalizations of right and wrong by rational means. but at least in America, I believe the prevailing sense of right and wrong at the moment doesn't require me to make statements against my own "values" or spend money, time or other resources making sure they get spread.
So it seems to me the problem with is argument is that it is based on an assumption that is both unproved and has considerable evidence against it.
Censorship and free speech are tools. They can both be used in ethical, legal and "moral" ways and used in unethical, illegal, and immoral ways. They are both dangerous and helpful. As an example the people who send death treats to people they disagree with on the internet are exercising free speech all be it in a way that is easy to argue is unethical, illegal, and immoral. If it was in my power to do so, I would stop them and I would be committing censorship though I would be doing so in a way that doesn't violate my ethics, could be considered moral could even be done legally if I was careful.
I think what you'll find however is that at least in America the general opinion has been at various times that the tool of censorship is far more easy to abuse. If someone uses free speech, I can always ignore them or attempt to convince them of my point. If someone uses censorship they can repress an idea from ever being considered and halt progress. We tend to think of censorship as more repressive and dangerous and are willing to put up with misused free speech unless or until the evidence that this particular exact piece of free speech is more harmful than expanding the use of censorship.
This is the same with how our laws generally require guilt without doubt as we find it more harmful to accidentally put a innocent person to punishment than let a guilty person off.
Nonetheless, censorship is an act of power. If I have the power to stop and or severely limit the spread of your thought, idea or expression and I exercise that power, I am censoring you. I'm sorry that is just what the word means. I just might not be "wrong" for doing it.
my 2 cents. Now get back to fighting over who censored who and is therefore both wrong in deed and therefore idea.
EDIT: Actually when i think about it the people who use death treats are exercising free speech in an attempt to censor which is a bit ironic.