A quote from the article:
"Facebook appears to be deliberately and systematically making it harder and harder for people to vary their self-presentations according to audience. I think that this broad tendency (if it continues and spreads) impoverishes public life. Certainly, the self that I present on this blog is very different from the self that I present in private life (I’m a lot more combative, for better or worse, in electronically mediated exchanges, than I am in person). It’s also very different from the self that I present on the political science blog that I contribute to. Both differ drastically from the self I present to my students. I don’t think I’m unique in this. And one of the things I like about the Internets is that I can present myself in different ways. This isn’t the result of a lack of integrity – you need to present different ‘selves’ if you want to engage in different kinds of dialogue."
So the author is suggesting that in general the internet is liberating in terms of identity and self presentation (so you can rowdy and rude on one forum, more kind and considered on another), but this in contrast with Facebook restricts this idea of fluidity in identity. Your identity isn't mediated - it isn't as selective and edited as you think.
Imagine Facebook being one room. In this one room are your parents, your siblings, your best friends, your teachers, your school friends, your girl/boyfriend, you pals from your football/hockey team - and they all want you to be the version of you they are used to. So you have to be rowdy with your football pals, be polite to your Mum and Dad, and be the romantic caring type to your loved one - everyone gets to see every side of you. You're exposed.
This is something Mark Zuckerberg, Facebook's creator, seems to be proud of:
“You have one identity,” he emphasized three times in a single interview with David Kirkpatrick in his book, “The Facebook Effect.” “The days of you having a different image for your work friends or co-workers and for the other people you know are probably coming to an end pretty quickly.” He adds: “Having two identities for yourself is an example of a lack of integrity.”
Perhaps he's right. Perhaps this stripping of privacy will become the norm so every break-up, drunken picture, emotional outburst, argument, birth, loss etc. will now be played out in front of your Facebook friends. But what do I care - I'm not on Facebook. Ha!
Here's another arcticle that contemplate the threat to our identity by the transition from a physical way of consuming media to a virtual one.