I’m kind of "split" on this one. On one hand, having been stalked and harassed before on a social network, I understand why some folks prefer to keep their profiles "private". And this is always a risk on social networks.
On the other hand, isn’t the point of joining a social network so that you can meet new people and share ideas and common interests. So, if you block your profile from being viewed, then isn’t that kind of defeating the purpose of joining?