The problem are the idiots who expect you to be on Facebook.
I have no problem with anyone wanting to use any social media or any other website (certain illegalities aside) . However, when they then expect you to have to sign up to, for example, see the pictures they took of their new baby or to organise a party -- then I have a problem.
As somebody who is opinionated and interested in contentious subjects I am as careful as possible never to use my real name or the real name of my employer (or anyone else) on the internet. This is so that if, for example, I post on El Reg something critical of the Pope I'm not then in the slightest bit worried if I happen to apply for a job which involves mowing some church lawns.
It could be said I could sign up to Facebook and only use it to view baby photographs and check event times but what happens when I don't use it for a year and it's hacked, the privacy settings change, or similar? You also have problems off cross-linking with other things if some twunt uses your handle along with your name or some such which are a lot less likely to happen when real names aren't part of the medium at all.
It also seems the height of pointlessness to sign up to something to not use it.
I love online discussion and find it actually helpful knowing the extent of views and opinions -- online debate has both changed and strengthened my views on many subjects. I doubt, however, that some subjects would even have been discussed with real names attached.