Why didn't the Order of the Phoenix destroy the prophecy?
- Dumbledore had already heard and memorised the prophecy.
- Though prophecies cannot be taken off the shelf by anyone other than the subjects of the prophecy, they can certainly be destroyed (Harry and co. did).
- It would have been safer. If the prophecy was destroyed, the Order would not have to literally sit in front of the door to the Department of Mysteries to protect it.
- I think it would be helpful because Voldemort still thinks it is important (even though we know it isn't) and if it was destroyed, he would know that the only way to hear it would be to get the memory from Dumbledore (the only wizard he ever feared).
I have never heard any convincing argument against this alternative and therefore am convinced that it is a plot hole, but would like to hear what you all think.