Straw Hat Luffy gonna destroy the Fishman Island? During the Fishman Island Arc, Madam Shyarly's in Coral hill predicted that a man with a straw hat is destined to destroy the Fishman Island. 
They say Madam Shyarly's prediction never failed. I can't  think of any other besides Luffy that is wearing that hat.

How can Luffy possibly do it? Because in the first place, he saved that island and he's not that kind of guy who will do such a thing. Also, Fishman island lies right underneath the Red Line and Mariejois. So destroying Fishman island means destroying the capital of World Government, Mariejois.

Questions:


How can Luffy possibly do it? (if he is the destined one because it lies beneath Mariejois and Red Line)
Could this be another straw hat guy? or her prediction is just wrong?
Strictly speaking there are at least 4 possibilities which are all possible:


Luffy's actions could bring about the destruction of Fishman Island due to his risky behavior.  For instance: he claimed it as his own and challenged Big Mom for it so she could destroy it and it would be Luffy's fault.
Someone could destroy it impersonating Luffy in order to turn his rapidly growing group of allies against him.
Luffy could change the island so much that it could seem like destruction. He could, for instance, bring it to the surface or promote desegragation of the world so an island inhabited by just Fishmen/Merfolk is no longer a thing.
Finally, Luffy could be forced to destroy it for strategic reasons such as might be required in the "alter the Red Line so there is just one Giant Ocean and the world can be easily transversed" fan theories.


Ulitmately though, we don't know what will happened and any theories are speculation.  The residents of Fishman Island have been convinced that Luffy will do them no harm, even though that is foolish, as Shyarly's prediction are reportedly never wrong.  We can assume from his character, however, that he will not intentionally do anything to harm Fishman Island without suitable recompense. We can also assume, however, that this important plot point will not be forgotten and Oda will provide an explanation in the plot at a later date.