I don't use my legal name on the Internet and I never have.
99% of my online friends know me by a pseudonym, and most don't know my legal name.
I use a pseudonym on Facebook and nobody seems to mind. Contrary to the belief of some, using a pseudonym does not inspire me to be crass, racist, bigoted, or just plain mean.
I use a pseudonym because I am a woman who has been stalked from Internet sources, all the way into concrete life.
Nothing scares you quite as much as the idea that some crazed Internet lunatic may be following you with a gun, intent on silencing you, once and for all.
If celebrities can use pseudonyms, why can't I? Do the celebs throw all common courtesy out the window because they're using one? Some do, I know - but they'd be just as crude and rude no matter what name they used.
Today I was reading an article on Google+ which shows just how naive some people really are, despite all the warnings and terabytes of information out there that it is NOT safe to use your real identity on the 'net. I saw some raise the issue of "What do you want to say that you're afraid to say under your real name?" for instance. Um...ever been an activist for some cause that has its detractors? Ever been stalked to the point where someone claims to have your real address and is passing it to others who could pose a real danger to you? Ever been divorced or have left an abusive partner that you don't want to have track you down? Those are just a few reasons why someone would post under a pseudonym and it has absolutely nothing to do with being afraid to own one's own words.
Basically, anyone who is not a white, privileged male from a Western country can find reasons not to use their real name on the Internet. Heck - even some of those have reasons. Ever say something on your G+ account that you wouldn't want a future boss to see, or your current boss to see? Ever bitch about something at work? Ever criticize some workplace policy, or lack of?
Those who claim that it's "right" to use your legal name on the Internet have obviously been lucky enough never to have been a target of others who would want to hurt them. Give it time; sooner or later, they'll say something someone else considers unpopular and it'll be brought to their attention at a most embarassing time.
I have used nyms since I got involved with the public Internet near its launch. Right from the start, you are told not to use your real name. Bulletin Board Systems expected you to use a pseudonym. IRC chat, the basis of all other popular chat systems today, expected you to use a nym. Kids are told never to use their legal name on the 'net because it could encourage pedophiles. How many young users of Myspace were bullied because they used their real name, and bullies found them? How many have committed suicide?
Do you really think that kind of behavior stops when people reach the age of 18? If so, you have a lot to learn.
I have known bullies who DID use their real names set about gathering a mob to drive someone clean off the Internet. I have seen others fall victim to such tactics, and worse.
It is a matter of personal safety to use a nym and I'm not about to change that for the benefit of ANY multinational multibillion corporation!