The crux of the argument:
Dr Sigman maintains that social networking sites have played a significant role in making people become more isolated.
Well! Consider the gauntlet thrown. Let us start with the fact that Dr. Sigman is male. I warrant he has never been trapped in the house for 2 months straight with 3 or even 4 kids under the age of 7 suffering from assorted ailments including - but not limited to - colds, stomach flu and chicken pox. In other words, Dr. Sigman does not even know what the word "isolated" means. Not the way we mothers know it.
As far as mommy bloggers (and I wear that label with pride) go, Dr. Sigman has put the fabled cart before the fabled horse. It is the damnable isolation that our jobs can impose upon us that drives us to find companionship (of the platonic variety, of course) on the Internet. Throughout the course of my parenting career, I have frequently endured weeks upon weeks of not getting together with close friends, due to their children's illnesses and schedules conflicting with my children's same. Until I found people to converse with over the Internet, I was at risk of going stark raving mad with isolation. Yellow Wallpaper mad...
What's more, I am in better touch with the people I know in real life because of my blog and Facebook. I've learned more about my grown nieces' lives in the past 3 weeks as their "friend" on Facebook than I've known in the previous 17 years. From reading my blog, my real-life friends know what is going on in my life, even if I can't pick up the phone (mothers learn quickly that trying to converse on the phone with children around is a surefire way for one or the other of our lovely offspring to incur an injury of ER magnitude).
The Internet has made us closer, not more estranged, Dr. Sigman. People are turning to the Internet to communicate because today's busy lifestyles have made it difficult for us to connect frequently otherwise. And to posit, as you do, that social networking sites reduce levels of face-to-face contact seems to be a bit of a logical jump. I have never turned down an opportunity to get together with friends because I wanted to stay home and blog or Facebook. Virtual interaction is for when there is no real interaction available. And those times happen frequently in a SAHM's life.
Now, if he had suggested that blogging and Facebook lead to child neglect, he might have been on to something...