These articles drive me crazy sometimes. A really valuable message is couched in fear of online social networks.
These same problems exist in every electronic medium. There is a persistent record. We will very likely see old Facebook videos used as evidence against Presidential candidates 10 or 20 years down the road, but we are more likely to see something pulled out of the Internet Archive well before that happens, since that is where the evidence exists on the pre-Facebook/MySpace crowd.
To say that this is a problem with online social networks is just ignorant. This is a problem with ALL form of publication (the Web is just a big publication machine).
We need to educate learners (of all ages) on how present ourselves online. We teach our children how to say please and thank you. We teach our children not to talk to strangers. We even teach our students not to run around naked outside. How about teaching children to respect others in online interactions, not to give out identifying information to strangers, and no to post potentially embarrassing materials online!
This is obviously not common knowledge and the blocking of these sites just removes the possibility of addressing these issues in schools.