I came across an article today that described this concept much better than I could ever done. While I am not sure that I agree with all of its conclusions, it makes the point that I have tried to very simply, so I will quote it at length:
The First Amendment is what everyone loves invoking. But of course the First Amendment begins with the words “Congress shall make no law.” And I didn’t see Congress passing any legislation here. Here’s the thing. Amazon is perfectly, legally justified in kicking customers off its service for any reason. They do have to realize that there are enormous PR implications when they do so. What Amazon is asserting here is that they are willing to remove content based on political pressure, or based on the perception of the offensiveness of that content.
What’s really hard about this is that we perceive the web to be a public space, a place where you should be able to go and set up your soapbox and say whatever you want to say to the world. The truth is, the web is almost entirely privately held. So what happens here is that we have a normative understanding that we should treat this like public space—that you should have rights to speak, that no one should constrain your rights—but then you discover that, basically, you’re holding a political rally in a shopping mall. This is commercial speech, controlled by commercial rules. My sense is that companies try really, really hard not to assert their corporate imperatives, and to say, ‘we’re going to silent speech,’ because that makes people really uncomfortable. But in this case, I think Amazon probably did a mental calculation and said, ‘if we don’t do this, we’re going to end up the subject of a boycott on Fox News, and that’s coming right before the Christmas season, we can’t afford that.’ I have no way of justifying that statement; that’s a speculation. But I understand why they might be concerned about this.The emphasis is mine. This passage is precisely the distinction I have been trying to make. All of your accounts (Twitter, Facebook, etc.,) are held by private companies who can suspend or delete your account for any reason or no reason. They are not violating your free speech rights, because you have no free speech rights in a private, commercial forum. As Ethan Zuckerman describes in the above passage, Twitter and Facebook are like shopping malls; and they control the rules. Have you ever seen those signs that prohibit photography in a shopping mall? That's because the mall owner can regulate the activity in the mall, including preventing you from taking photographs. You might think that's an infringement on your free speech, but you'd be wrong. Lastly, your ISP can do the same thing and suspend or cancel your account for any reason or no reason at all. You have the right to free speech, but that doesn't mean you have the right to Internet access or a Facebook or Twitter account.
This very post, on my soapbox, is contingent upon terms of service by my ISP and by Blogger/Google. as much as I like to think it is me practicing my right of free speech, in reality it isn't. If it somehow violated their ToS, or if they just didn't like me, they have every right to remove the post or suspend my account. It would be similarly disappointing, but I couldn't sue them for violating my free speech and expect to win.
Update/clarification: After some further reading I guess I owe a bit of a clarification. It is certainly true that from the perspective of the government, your Internet speech is protected (ACLU v. Reno). But from the perspective of a private business, there is no such protection. I recognize this is a messy distinction, especially when a government "pressures" a business to do something or other, but it an distinction that exists nonetheless.
Update 2: This article by Brad Templeton discusses spam, but it touches on the same issues: "the collision between three important rights -- freedom of speech, the right to control private property and the right of privacy."