Read about the decision here.
Read the decision, written by Justice Kennedy, here.
Social media allows users to gain access to information and communicate with one another about it on any subject that might come to mind....By prohibiting sex offenders from using those websites, North Carolina with one broad stroke bars access to what for many are the principal sources for knowing current events, checking ads for employment, speaking and listening in the modern public square, and otherwise exploring the vast realms of human thought and knowledge. These websites can provide perhaps the most powerful mechanisms available to a private citizen to make his or her voice heard. They allow a person with an Internet connection to “become a town crier with a voice that resonates farther than it could from any soapbox.” Reno, 521 U. S., at 870.
In sum, to foreclose access to social media altogether is to prevent the user from engaging in the legitimate exercise of First Amendment rights. It is unsettling to suggest that only a limited set of websites can be used even by persons who have completed their sentences. Even convicted criminals—and in some instances especially convicted criminals—might receive legitimate benefits from these means for access to the world of ideas, in particular if they seek to reform and to pursue lawful and rewarding lives.