Deny Message History Permission - Hide All Messages

The current rule for denying "Read Message History" makes almost no sense to me.  

If this permission is disabled, members only see messages sent when they are online and focused on that channel.

If you are denying message history, why would you let them see messages?  What difference should it make when they accessed the channel?

We need a permission to hide all message history.  This is especially useful for a helpdesk channel so members can post complaints or ask for help (i.e. Send Messages is allowed) without being able to see other people's posts so admins/mod roles can handle them.