Eliot wrote this poem during the Modernist era, a period in literary history following WWI. The poem deals in death and dying, a common response to a world that has seen more than its fair share of both. The poem is set in April, which is described as "the cruelest month." Traditionally, April evokes images of spring and rebirth, but Eliot gives us a garden that has been planted with the seeds of devastation. In lines 71 to 73: "That corpse you planted last year in your garden, 'Has it begun to sprout? Will it bloom this year? 'Or has the sudden frost disturbed its bed?"
In order to answer your question, you must first consider why these images permeate Eliot's work as well as the works of other Modernist writers.Modernism came about as a reaction to WWI and the social conditions (particularly the working conditions) in the United States. It moved away from Realism (which presented ideas as closely to reality as possible) and stressed fractured and disjointed ideas. The "real" was still there but it was made more vivid. Additionally, three schools of thought emerged - Freud and his ideas of psychology, Marx and his ideas of social class structure and repression, and Nietzsche whose own philosophy was based around fragmented bits of great epiphanies of thought. All three philosophers saw that the world was falling apart - crime, brutal working conditions, poverty AND a war that had torn the world apart led to an overall sense of disillusionment - the world as a whole was often referred to as a Wasteland at this time, and Eliot's poem has later been alluded to in other works as symbolic of the imagery of the world as a wasteland.
With all of this in mind then, you must consider this - is this a poem of disillusionment, or is the sense of fracturing and isolation, hopelessness and despair, an overt call to examine this world and pit things right again? Keep in mind that Eliot did not write poetry for the masses - he wrote for an educated elite who were literate, sophisticated, and would easily understand his rhetoric. As such, while YES, this is a poem of disillusionment, it is also a poem of conscience.