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Online businesses exercise increasing control over what we say, what we read, and what we share online.

In Monday's New York Times, about ways in which large Internet companies such as Facebook, Google and Yahoo are increasingly using what they know about a person to decide what content to show that person. A search engine may use a person's past search terms what results to display in response to future search queries. For example, if you've searched for flights recently, querying "Egypt" might yield tourism information instead of news about the revolution.

It's not just that search results are being tailored to particular individuals. It is also that content that used to exist on the open Internet has migrated to proprietary systems such as Facebook, which restrict speech in ways the government cannot. For example, Facebook that "contains nudity." The government cannot censor mere depictions of nudity, and of course feature nudity. This is not a hypothetical problem. Facebook removed from the 's Facebook page. It has removed as well.

While there isn't anything wrong with a person making a knowing and voluntary choice to join an online community that places restrictions on speech — and in fact, the First Amendment protects the right to associate free from government interference — it's worrying to think about the possibility of these closed systems hollowing out the freer speech realm of the open Internet.

As the Supreme Court when it struck down Congress's first attempt to censor the Internet, "the content on the Internet is as diverse as human thought." We should take care that this defining characteristic of the greatest forum for free speech ever invented isn't whittled away through millions of private choices whose cumulative effect no one would desire.

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