So here's my opinion for what it's worth - we do have to empower children with knowledge and understanding of the Internet, and what playing in a place where everyone can be watching really means.
But - we are just now really learning what the read/write Web fully means - and there is a huge amount of untapped possibility for every classroom that exists right now. A lot of it is for free (now at least.)
If you think back to the early days of the Web, so many of us were enamored with just putting up simple Web sites, and with finding things online. People put up lists of clickable links and aggregated all sorts of Web resources ad nauseum. Sometimes the links worked, sometimes they didn't. There are still lots of pages like this out there.
But now interactivity rules. Newspaper articles have comment areas. Experts on just about everything blog. Podcasts from conferences are available days after the event. Wikis on any topic are there for the reading and for the editing. It's the world now.
Social networks are important in my opinion because community is changing and shifting and because communication, real give-and-take discourse, can happen that didn't happen with the flat Web and its lists of resources. It's the discourse that's important. How does that discourse happen, what is shared and what shouldn't be shared, how does living publicly in networks make or break reputations, enable or thwart learning, add to or warp knowledge, how can money be made and influence be obtained, what is kindness in the age of Web 2.0.
There are a lot of questions and the people posing these questions and ideas? Teachers. Because we have to.