Another weapon in the left´s war on America....
To be realistic, Facebook is a global enterprise.
Most facebook members are not US citizens because most people on earth are not US citizens and Facebook is sort of a global picture. The rest of the planet has largely slid further into paganism than we have, so one would expect the site to mirror that.
The main reason to stay away from Facebook is that they are marketing all your private information that they promise to keep confidential when you sign up.