Because this "choice" restricts freedom of other people. You don't just want it to be a secret (then all you have to do is not to tell anyone), you demand that other people to respect and enforce it to be a secret (restricting other people's choices by restricting information).
If I give you three choices A/B/C, and don't tell you which is which, do you have a choice or not? I would argue that you don't. You need to understand what's behind each choice to be able to "have" a choice.
