Board Thread:Spoilers!/@comment-5899967-20151007105826/@comment-6175354-20151007115814

It was either Merlin of Arthur who put Excalibur back into the stone. If Merlin did, it was to keep the sword from Arthur. If Arthur did, it was to keep it from Emma.

Considering Emma is trying to manipulate Hook, he probably did not contribute to her embracing the Darkness. Along with Henry, Hook is the only one she believes qualifies as a hero.