Did the Sword of Gryffindor become a dark artefact when it was imbued with Basilisk venom?
Now I don't have an opinion one way or the other, but if you take the time to consider the following bit of conversation between Rufus Scrimgeour and Hermione, Hermione says something interesting:
‘The Decree for Justifiable Confiscation gives the Ministry the power to confiscate the contents of a will –’
‘That law was created to stop wizards passing on Dark artefacts,’ said Hermione, ‘and the Ministry is supposed to have powerful evidence that the deceased’s possessions are illegal before seizing them! Are you telling me that you thought Dumbledore was trying to pass us something cursed?’
Deathly Hallows - pages 104-105 - Bloomsbury - chapter seven, The Will of Albus Dumbledore
Could the Sword of Gryffindor have become a dark artefact once it became impregnated with Basilisk venom? It seems only magic from the dark arts can destroy a Horcrux, the ultimate dark artefact, and the Basilisk is a deadly, dark creature, and its venom undeniably evil. Is it logical to suggest the sword, then, was turned from a mere Founders heirloom to a dark weapon?