I agree with this.
The Sword that was Broken has passed down from father to son for
ages. It has finally been reforged!!
Aragorn probably has slept with the broken
sword by his side ever since
Elrond gave it to him and told him his heritage. Not only is it the sword that cut
the ring from
Sauron's hand, it's one of the few things that Aragorn has from his father.
I don't believe Aragorn's words were a direct threat, per se, that he, himself, would kill anyone who touches the sword (although he may want to)
I believe it's more of a pronouncement of the probable consequences of someone who draws the sword. Not necessarily a curse, or a prophecy. It's more than an important heirloom, it's a
symbol of a possible united kingdom of
Arnor and
Gondor. Someone who takes the sword and tries to unsheath it is doing more than simple thievery. That person is dishonoring
Numenor.