Isn't that reason enough? Or to protect any other potential buyer, the current owner, any passengers (s)he might take up, and promote a general safety-conscious attitude? In another thread, there's shock that someone might fly a plane with a known deficiency without a special ferry permit. Here, we've got a possibly damaged aircraft with the potential of the damage being swept under the rug, and everyone is advocating to turn their head and ignore it.
Let me put it this way: If you witnessed damage to a commercial aircraft you weren't a passenger on...say, a baggage cart rammed into an engine nacelle... but the cart driver didn't say anything and nobody else noticed before departure. Would you keep your mouth shut, and if not, why is this any different?
