Why? Most users really don't understand the consequences of the default settings, let alone which checkbox has which effect.
Just the other day I was browsing CNN and to great surprise a section on the site named a HN user as recommending that I should go and check out some link. Turned out it was powered by facebook and I had made the mistake of not logging out.
That's something that won't be happening again, but I'm not sure I could have predicted that sort of thing would happen.
And I'm definitely not comfortable with it.
For me, facebook has changed from a place where I share some stuff about me with my friends to a shingle for people to get in contact with me through other means.
I will not delete my account because that is a useful function, but my facebook days as an active user are mostly over (not that anybody cares or should care).