Are we entitled to data security?

In a Wall Street Journal article related to Twitter's settling of a privacy-related case, Consumer Protection Bureau Director David Vladeck states:

Consumers who use social networking sites may choose to share some information with others, but they still have a right to expect that their personal information will be kept private and secure.

If I, as a consumer, choose to create an account with a free social network service like Twitter, why am I entitled to anything beyond the terms of services to which I agreed?