Private post option not showing for guests

If I am logged-in I can see the checkbox for private posts (like the one above on this page):
"[ ] This post will be private and it can only be seen by you and the support team members"

If I am a "guest" and am not logged in, I do not get the option of a private post.

I have been through the configuration several times and must simply be missing something. Can you please point me in the correct direction?

(If a visitor comes to the website and cannot log in - I would like to give them the ability to use a private post "ticket" to send a message and receive a reply on how to fix his/her issue.)

Thank you in advance!