So, consider "Hey, tomorrow is angersock's 34th birthday! We're organizing a surprise party in his hometown of jonestown!".
Now, they've given away my age, birthdate, and where I was born. That's the sort of information that, while private and something I don't give away, they know and give away without thinking.
Who is it you don't want to have that information?
The government already knows (it's part of your SSN information), and any private company that cares will just make you give that info to them as part of the cost of service. You'll do it too, because you don't want to be unable to drive or have a mortgage.
I know about those entities, though--and I know that, in the case of private companies, they're probably going to share it (and we can make laws to that effect).
My original point is that those protections won't apply when just crawling through friends and acquaintances mentioning things.
EDIT:
For another example, consider "Thank God, my friend angersock had a car accident today but only scratched the bumper". That's something I don't want as public knowledge, and that my insurance provider could (theoretically) use to raise my rates.
Also, revealing your birthdate to the general public could help people convince your bank they're you, or bust a pseudonym that you had been trying to keep separate from your legal name.
Now, they've given away my age, birthdate, and where I was born. That's the sort of information that, while private and something I don't give away, they know and give away without thinking.