It’s not for the receiver to keep them from knowing you read it, it’s to build a queue of messages you want to reply to (anything unread will be easily marked in the UI for later revisiting next time you get a text or open the app). In this case, marking it unread wouldn’t need to affect the read receipt in any way. Really the unread feature is an ad hoc reply reminder flag.

Ooooh I see. Thanks for the clarification