Even the wise cannot see all ends, I think that as the shadow of Mordor stretched over the land once again the sight of even Elrond was diminished unable to see what end awaited the quest for the destruction of the ring. Especially as so much of the quest lay with chance even up to the destruction of the ring itself by Gollum.
As Superguy explained, the scenes from R.K. were all pulled from P.J.'s arse. I enjoyed the films, but disliked the unnessecary fantastical/Hollywood-additions, (e.g., whiny-Elrond, Legolas' acrobatics, etc.).
That being said, an explaination for the scenes of the film could be: Elrond didn't want his daughter to live the life he knew she was doomed to live if she married Aragorn.
If I may quote an essay I've read, which deals with the subject of sex and libido in the works of Tolkien, there is a passage that deals with the union of men and elves, and in conclusion to the unhappy story of Aragorn and Arwen, the author comments: "(...) [Arwen] seems punished, somehow. Aragorn's choice of death plunges her into a sad understanding of human denial of death and leaves her without reason to live. Arwen's descision to remain in Middle-earth and love Aragorn, motivated by passion, becomes hollow, in the end," (Tyellas, Warm Beds Are Good: Sex and Libido in Tolkien's Writing).
She then quotes Arwen from The Tale of Aragorn and Arwen, (R.K., Appendix A), to show evidence for her statement: "I must indeed abide the Doom of Men, whether I will or I nil; the loss and the silence."