It isn't. The full name, including everything after the @ is the name of the community. They act differently and should be treated different.
To put it another way using email as an example, we wouldn't treat [email protected] as the same as [email protected].
There were experiments a few years ago that attempted to see if some primates could learn the concept of money. A coin could be used in exchange for a piece of fruit. Some primates were able to understand that the coin represented fruit.
Those primates discovered prostitution soon after.