[srbloom]

Let's not get caught in a false dichotomy. Not having a Facebook does not necessarily make you anti-social. But if we take "anti-social" to be a measure of one's social availability, not having Facebook decreases that measure. Communicating only by smoke signal or carrier pigeon would make you extremely unavailable whereas communicating by email and telephone would make you very available. In some demographics, users check their Facebook 3+ times per day, so depending on your social circle, being on Facebook makes you highly available.

For the record, I do not use Facebook, but I accept that it makes me less available. Friends who make Facebook events to organize events can invite nearly everyone they want to invite to their event on Facebook, but have to go out of their way to invite me via different means. This makes me anti-social to some (pretty small) degree.