Richard Posner writes,

The second motive for privacy, however—the desire to conceal discreditable facts—is more questionable from a social standpoint. In order to make advantageous transactions, both personal (such as dating or marriage or being named in a relative’s will) and commercial, people try to “put their best foot forward.” Often this involves concealing information that would cause potential transacting partners to refuse to transact with them or to demand better terms as a condition of doing so. Such concealment is a species of fraud.

He argues that the case for medical privacy is limited. While people with no need to know your medical history should not be able to peruse it, Posner argues that the law should not help you to conceal your medical history from, say, an insurance company.