I am curious why this is supposedly creepy. I think the main premise of a social network is that you reach out or get reached out to people who might know you or you might know. Now, you have the option of not reaching out to those people, and I think it is fair game that the social network assumes that other members might reach out to you, a member of the network.
If you do not like that aspect of the social network, do not join it.
Educated guesses are one thing; exact "guesses" are quite another, and one has to wonder where the 'guessing' is pulling its data.
Would it creep you out if I guess which month you were born in? Probably not.
Would it creep you out if I guessed your exact birthday, including month/day/year? Hell yeah it would.
It has nothing to do with whether or not one wants to be social, and everything to do with random, axe-murderer creepiness. Imagine if I walked up to you at a party and rattled off names of 5 random people from different aspects of your life; would that not freak you out? "Oh, you don't know me, but I know you ;)". That's virtually the same thing that is happening here.
If you do not like that aspect of the social network, do not join it.