Interesting question.
From my own thoughts, I would say that
Elrond, and honestly almost all of the
Elves had a certain sadness, a certain dryness that could theoretically be considered cynical. That most likely came from a few things.
Firstly, the Elves in
Middle-Earth were not in their homeland. They were first in
Valinor, and dreamed of the far-off country they would hopefully one day enjoy. Knowing that the life that they were living was merely a journey, and that in it they could never find true contentment and everlasting fulfillment, their outlooks may have had a dimmer and less joyful feel.
Not to mention, Elves were very much grievers. We can see that just by the number of laments that they have alone. They clearly felt a deep need to grieve and weep for the fate of the world, and to honor Middle-Earth and the lands beyond, by their tears. Elves were spiritual, in more ways than one, and so grieving, mourning for the fall to darkness, seems very in character for them.
Secondly, they, especially Elrond, had seen many
ages of the world. They saw
battles won,
wars, the rise and fall of
kingdoms. They saw the corruption of power, and watched good leaders of
men turn their backs on the goodness in the world and become obsessed with power and wealth. Elrond saw
Isildur fall to the fate of
the Ring, and so the Ring's power would have held a very personal darkness for him.
I think Elrond was just being frank and realistic, as well as warning them not to get too attached to victories and power. In your first quote, Elrond is almost saying that he has seen defeats and victories, and both can be just as fruitless. In my opinion, that's a valid point, especially because men can become thrilled with conquest and ruling, and completely forget that none of those things are the point of life. Elrond had also lost his parents at a young age, and that no doubt colored the way that he viewed the world. Especially being raised by
Maglor, a very flawed individual, and flawed mainly for the reason of his father, and wanting power. Elrond would see just how many times power led to victories but defeated the good of the soul.
As for the second portion of your question (Quote 2):
I honestly don't think that this is cynical at all. The story of
Beren and
Luthien is a beautiful one, and no doubt the first one that would come to mind when Elrond realized his daughter's heart was set on
Aragorn and his on her. But even in all its beauty, it is a terribly tragic story. While Luthien's lamenting and
Mandos' pity are touching, the ending still comes with death. The immortality of the Elves was not Beren and Luthien's fate, and they tasted bitter mortality before the end.
Elrond, being a good father, would not have wanted this for his daughter. He would have wanted
Arwen to wed an
Elf and go on living immortally. He, himself was
Half-Elven, and that also might have played a role in his desire for Arwen not to marry Aragorn. His being half-elven, no doubt set up challenges for him, one of which being that his brother, choosing mortality, died. By the point of the Fellowship of the Ring, his brother was dead. And he would have known that his brother
could have lived, had he chosen the fate of the Elves.
That brings me to my final point, Elrond's own motives may also have been involved in this desire of his, and in his saying of this quote.
Elrond had seen many of the people who he loved taken from him throughout his life. His father and mother being the first, and then later Maglor who fostered them, and later farther, his brother
Elros, and eventually his wife
Celebrian. Each one of those would have likely been very painful for him, and he may have wanted no more death for their family. His daughter, Arwen was the only one still actively living beside him as mentioned, and also seems very close to him in the
books, so he may have just not wanted to lose her.
Again, these are just my thoughts.
