There are many
instances in which using your real name on the
internet is either A) Stupid or B) Unneccessary. The internet IS a
fantasy alternate world, in fact. It might be
digital, you might not have a
body, you might only be able to access this world via the
monitor on your desktop, but does that make it any less a
world?
And to provide a writeup that's not just an argument...
The act of using your real name on the internet is one practiced by people who A) feel they have nothing to hide, or B) don't have the imagination to come up with a good username. This is the converse of using an assumed name (An Alan Smithee, if you will), used by people who A) just think it's a cool name to use, or B) are paranoid. Either form is acceptable under certain circumstances.