This simply isn't true - your most sensitive information is not public, yet is shared with 3rd parties. From their privacy policy:
"We collect location information about you including your IP address, your location, browser information, and how you came to the Stack Overflow Network."
(SO also collects your email address, interests, and employment status upon registration - this is not mentioned specifically in the privacy policy)
"This is the case for individuals who have registered for an account, and non-members who engage with the Stack Overflow Network by visiting our website(s) but who have not completed an account registration."
"We share this information with certain third-parties (e.g., talent recruiters, payment processors, and advertising providers)"
"We collect location information about you including your IP address, your location, browser information, and how you came to the Stack Overflow Network."
(SO also collects your email address, interests, and employment status upon registration - this is not mentioned specifically in the privacy policy)
"This is the case for individuals who have registered for an account, and non-members who engage with the Stack Overflow Network by visiting our website(s) but who have not completed an account registration."
"We share this information with certain third-parties (e.g., talent recruiters, payment processors, and advertising providers)"
https://stackoverflow.com/legal/privacy-policy