I think the distinction is "reach". Emails are generally directed to dozens, maybe hundreds of individuals, whereas with modern social media, an individual can reach millions of people. It begins to enter the realm of traditional media organizations.

But unlike traditional media organizations, there are far fewer laws in place regulating the responsibility that comes with that reach.

It is an interesting problem, and I'm not sure there is a good solution, other than try to combat it head on with education (how to properly evaluate the information you accept), and possibly PSAs.