I disagree. Former classmates often share quite a bit. There's likely a slightly greater level of trust and accountability than with a total stranger, and there's a good chance it'll be easy to find a topic of conversation to start with. I also know that I, personally, would be more likely to do a small favor for a former classmate than a complete stranger. For example, if I knew via facebook that one of my former classmates was an Erlang programmer, and one of my other friends was looking to hire one, I might try and hook them up. I wouldn't bother to go looking for random stranger Erlang programmers.

Being former classmates isn't like being close family, but it doesn't mean absolutely nothing either. It's a minor but significant reason why you might want to connect with someone using facebook. A similar minor but significant reason might be that you just met at a party last week and seemed to get along really well.

And again, the point is that there's usually nothing to get creeped out about. If you'd rather focus on new friends and forget old ones that's fine, but an old connection isn't absolutely nothing.

Incidentally, I consider the word "creepy" to have more of a threatening connotation than simply annoying and unpleasant. An old, dark, abandoned house is creepy, you don't know what's inside and it might be threatening. A guy is creepy when he doesn't know a girl but stares at her for 20 minutes at the bar then follows her home. Reconnecting with old classmates who have fallen out of touch is not creepy, at least not by default.