While doing Social Sign On of Facebook I am getting this error

Object Id  is any but unique.(email, user name_org suffix .. etc)

which will return while you login in  during salesforce SSO.

i suggest you follow this video and code.

the code will create the users automatically.

https://www.youtube.com/watch?v=vsrl8bo1r1M

https://github.com/salesforceidentity/IdentityTrail-Module3/blob/master/SimpleFacebookRegistrationHandler.cls

in Azure Active Directory. you can create multiple objects. 

this objects will return during the login. 

the difference is here Azure Active Directory is easy to use out of the box. 

but Facebook is, you need to code.

i hope this helps, 

thanks.