You have one identity. 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 … Having two identities for yourself is an example of a lack of integrity.
This is exactly the kind of thinking that corporatists always have, because it assumes that you must be your job. The belief that people have one identity is false on its face, with so many obvious counterexamples that it's almost embarrassing to have to point them out. People behave differently in different groups and under different circumstances, but our corporate masters would rather you be in your work persona at all times. And they are willing to hold future employment ransom to achieve this end.
Mark himself doesn't have a problem with this because he doesn't actually use his facebook account as anything more than a personal advertisement, and the great likelihood is that he doesn't even maintain it himself. The amount of personal information posted there is minimal and that fact is quite telling about the actual intention of the site; if it's (supposed) creator doesn't even use it for its advertised purpose, then the actual intent must be something else.
If Mark's attempt to control commentary on the Internet succeeds, and big sites buy into it - specifically, that you must be logged into FB to comment on any major website - then a very broad range of people will never be able to post any commentary on controversial issues, ever, because doing so will eventually negatively affect their career. Teachers could never, for instance, take a position on religion in the classroom, or evolution versus creationism, or abortion rights, because these statements would be directly traceable back to them. Technical people like myself could find themselves fired, and unemployable, simply because they gave positive or negative commentary to some competitor's products, or they took an unfavorable position on patent law.
Combined with invasive authoritarian behavior - like shown in this case, where school administrators had to force their way into a group-locked FB post - it is unsafe to post any kind of criticism, abusive or not, on any social website without some kind of plausible deniability, forcing people to post everything anonymously or not at all. (On a side note, if the discussion that caused the suspensions/expulsion in this case had happened in the football locker room instead of on Facebook, the kids would have simply been told to shut up or given detention at worst. The world REALLY needs to get past this distinction between written words being some kind of more serious speech than spoken words, especially when those written words require specific passwords to read.)
My approach back on CC was different - everything had to have a name associated with it, and it was not permitted to use someone else's name, but the name did not need to be traceable back to an individual. It was a partial anonymity, designed to foil trolls and imps but still allow people to have controversial positions on things without affecting the rest of their lives. It worked.
What Facebook is doing here is the exact opposite of that and, unsurprisingly, plays directly into the hands of powerful interests who value their need to keep their reputations free of criticism, more than they value your right to criticize.