Fake profiles are prohibited on FB in their TOS.
As long as the fake I.D. is not using someone elses's identity I do not think it is a crime, and I do not think FB would do more than kick the posts off the site. However, if FB wanted to make an example out of someone, they could sue them and cost them thousands in defense fees alone. (Whether they win or not, getting dragged through the system is expensive and heart wrenching.)
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