The American public does not have a right to know about the medical issues of celebrities because they are protected under HIPPA laws and have a right to confidentiality and privacy. There are many valid reasons why celebrities would not want the general public to know about their health status. It could be embarrassing or damage their careers.
A celebrity has just as much right to privacy as anyone else, especially in regards to their health. There is no reason anyone would have the right to know that she has MS. That is her own private health concern that she must deal with in the manner that she chooses, and if she chooses to make it public (which she did) that is up to her.
It is a celebrity's prerogative whether or not to disclose medical issues to the public. A celebrity is a human being, first and foremost. The medical information should be private, just as a private citizen's medical information is private. However, I do applaud Jamie Lynn Sigler for bringing more insight and attention to the condition of MS.
When a patient goes to a doctor, they expect their medical condition and all records to remain private. Only a data breach can result in the leaking of this information. If a doctor talks to someone else about the patients medical issues, they should be held accountable and face severe penalties.