Why are people so eager to publicly share everything about themselves on Facebook?

Is it ego or stupidity? Or both?

The things people share are obnoxious. Facebook catalogs everybody you know and exactly how you know them. It knows when you were born, where you went to school, where you grew up, where you currently live, where you work etc. It has current photos of you and all your family. It knows if you’re single, married, Atheist, Christian, Jewish, Muslim etc. Plus, it knows all the other crap that you post about your personal life. This is all out there for the public to see, not just your friends. I know there are privacy controls but people rarely, if ever, use them.