That’s not what this plugin is meant for. The use cases are to keep the users responses hidden for each other, and often only on a temporary basis. The topic author can be a teacher or a seller or something and must be able to post with additional information or such.
If there needs to be a private conversation then you will need to use private messages, and if they contain any kind of medical or confidential information then you would need to use the discourse-encrypt plugin as well. You might want to look at Create a link to start a new personal message with pre-filled information