"Public information => no need for privacy" is a very typical logical fallacy. Privacy is not a black-or-white thing, categorizing things into private/public misses the point.
For example: when you move out of your home, your location is public information. Anyone who can see you knows that you're there. Similarly, your "image" is public information, anyone can take a picture of you. This does not violates your privacy, as long as it happens by random people in the street. If someone tracks your every movement, takes a picture every minute and publishes this information on the net, your privacy is clearly violated.
I don't care that much about the SID thing, but people have every right to feel that their privacy is violated by automatic collection of data, even if the data are "public". Privacy has a lot to do with who has access to the data, what it does with it and even how easy the access is.