Why do they do it?Edit
Posers pose as other people because they may want virtual fame. Although some people pose to give the REAL user a bad name.
Is it against the law?Edit
Well actually, if you pose as someone using their real name it is indeed against the law. Example: On fantage, Mo Mitchel's name on fantage is tree66. Someone may pretend to be tree66, but is on a virtual game in which that will most likely not harm Mo. But if someone had a youtube/facebook account are pretending to be Mo and making them look bad, it can be punished by law.
Is it illegal to take someones video and call it yours?Edit
Absolutely!! This happens alot too. You should never steal someones fantage drawings and say their yours, thats like stealing the Mona Lisa from a museum. Pretty much stealing ANY video someone made and calling it yours is illegal. Dont pose.