Elrond, why?

Isuldor was a powerful man, noble in sprit and mind. Elrond could not just say "Do as I say pathetic mortal", the whole thing was about choices, free will and not being subjected to the demands of another (for that was Sauron's desire to dominate all other living creatures).

Another consideration was that Elrond had some inkling of the power of the ring and thought that he may be unable to destroy it and therefore sought for a pure spirit to do the deed. I do not think the second option is viable, but then again, one never knows with pointy ears.