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I like the idea, if ... given only to Owners and Moderators with theYes, I believe that was the intent, similar to Locking or Moderating a topic.
The ability to hide individual messages can create confusion when theTrue, but the use case I see for hiding just a single message would be in an otherwise valuable and/or important topic where just one or a few offending replies were made. Most likely, as in the OP's use case, the offending messages are destined to be deleted, but for whatever reasons need to be kept temporarily.
I leave it to the moderator to judge which is the better remedy (hiding the message(s) or the whole topic) based on their knowledge of the circumstances at hand.