...but if I have a friendship with you that I want to remain private for some reason, and you make it public, you are going against my wishes, you are a bad person, and you shouldn't do that.
This can often result in injury or death to the person who typically has a good reason for keeping their relationship secret.
I have a friend who is dating two women, neither of which who knows about the existence of the other. If he was to tell each woman, please update your Facebook privacy settings to keep our friendship a secret, they would rightly be suspicious. If them finding out about each other results in injury or death to him, it's not Facebook's fault.
This can often result in injury or death to the person who typically has a good reason for keeping their relationship secret.