'There is malice in this sword. The heart of the smith still dwells in it, and that heart was dark. It will not love the hand it serves; neither will it abide with you long."
—The Children of Húrin, J.R.R. TolkienThe father of modern fantasy fiction (is Dunsany the grandfather?) has addressed this issue at length throughout his works and it stands amongst the other statements he's made about craftsmanship and its relation to magic; the heart of the smith still dwells in it, warns Melian. Beleg Longbow knows, but takes the sword anyway. Unlike Stormbringer, say, the malice in Tolkien's blade is not inborn to the nature of the thing, but rather the effect of its creation. The sword Anglachel is literally cast with the intention of its craftsman embedded in it, permanently marred by the thoughts of its creator. I should add that, at the very end of the Children of Húrin, the sword does indeed speak, to urge Túrin to his death and cleanse it (and thus him) of the murders he's committed with it.
Thoughts are powerful in the legendarium. Elrond can cast his thought wide over the earth and Melkor's very thought hounds the children of Húrin and leads them to their doom. The world of Arda is itself a physical manifestation of thought (as embodied in the music of the Ainur). "Spells" and "magic" are songs sung with a particular intention. Thus, the bending of intention and thought is the primary magical agent in Arda—not that those who understand it even make the distinction between natural processes and so-called magical processes.
What's my point here? I'm not certain, save that the malice in the sword is great. I've generally explained cursed items in D&D this way—for example, the Sword of Orne, borne by generations of goblin-killers, which cannot now be sheathed in the presence of goblins and will never allow the wielder to retreat when fighting its hated foe was not originally so cursed. Centuries of war and hate poured into it, and the intention of its wielders shaped it into the weapon it is today.
This is almost a form of animism; things acquire anthropomorphic traits (like emotion) by being dwelt upon by thinking beings, by being used with intention. The idea that people cast their intention into the world itself is a powerful one, and serves Tolkien well.