I definitely agree. If you read this excellent poem lamenting the assassination of President Abraham Lincoln carefully, you will see, apart from the many instances of images and words that convey the poet's shock and sorrow about the death of the President, many images that also celebrate the rebirth of life and nature's natural cycle. Note first of all that the poem is set in spring, an obvious time of rebirth and a celebration of the cycle of nature as life emerges. Note the following quote from the first stanza:
O ever-returing spring! trinity sure to me you bring;
Lilac blooming perennial, and drooping star in the west,
And thought of him I love.
It is as if the meditation on death that this poem represents places our lives in the scheme of the natural cycle of life. As we read through the poem we see many more such examples that celebrate life and the rebirth inherent in nature. Every leaf of the lilac plant is said to be a "miracle" as it grows and blossoms, just as the poet mourns the death of his friend. At every stage, death is coupled with new life, as in the following stanza:
Over the breast of the spring, the land, amid cities,
Amid lanes, and through old woods, (where lately the violets peep'd
from the ground, spotting the grey debris;)
Amid the grass in the fields each side of the lanes--passing the endless grass;
Passing the yellow-spear'd wheat, every grain from its shroud in the dark-brown fields uprising;
Passing the apple-tree blows of white and pink in the orchards;
Carrying a corpse to where it shall rest in the grave,
Night and day journeys a coffin.
Note here how there is ample evidence of the phoenix-like qualities of nature. Violets are emerging, the wheat is "yellow-spear'd" and growing, the apple trees are blossoming, all alongside the corpse that "shall rest in the grave."
Thus in this poem it is clear that Whitman is keen to set this tragic event against a wider framework that celebrates life and affirms it. This is not a mere lament, but a poem that talks about the cycle of life and how the world continues and how often death is coupled with life.