Why add another answer when two very good ones have been offered to this question? Because it appears that the people making this claim overlooked two important details:

1. "The Waste Land", as it was published, owed much of its final form to the editorial attention of Ezra Pound. This is a well-known & established fact. Further, Pound was a major literary figure in close contact with the other major literary figures of his time: for example, he aided James Joyce in getting A Portrait of the Artist as a Young Man published. So he was very aware of what other poets had produced, & if there is any plagiarism in this poem, Pound would be equally guilty -- at the least for failing to prevent Eliot from committing this crime. (And there's no reason to excuse Pound as a partner in this crime: he was later enticed by fringe economic theories, & became a notorious anti-Semite & Fascist. Plagiarism would be a minor blemish in the reputation of this influential personage.)

2. And if Pound alone is responsible for plagiarism, we should limit ourselves to "The Waste Land" before Pound worked on it. This version of the poem is easily available for the manuscript has survived. An edition of this manuscript was published in 1974 as The Waste Land: A Facsimile and Transcript of the Original Drafts Including the Annotations of Ezra Pound, and the manuscript itself can be viewed at the British Library. (Here is an online copy.) I don't see any evidence that the advocates of this theory worked from this version of the poem, instead of the later final draft.

And by ignoring these two points, those who argue for Eliot's plagiarism weaken their case with poor scholarship. At least in my humble opinion.

It appears that the people making this claim overlooked two important details:

1. "The Waste Land", as it was published, owed much of its final form to the editorial attention of Ezra Pound. This is a well-known & established fact. Further, Pound was a major literary figure in close contact with the other major literary figures of his time: for example, he aided James Joyce in getting A Portrait of the Artist as a Young Man published. So he was very aware of what other poets had produced, & if there is any plagiarism in this poem, Pound would be equally guilty -- at the least for failing to prevent Eliot from committing this crime. (And there's no reason to excuse Pound as a partner in this crime: he was later enticed by fringe economic theories, & became a notorious anti-Semite & Fascist. Plagiarism would be a minor blemish in the reputation of this influential personage.)

2. And if Pound alone is responsible for plagiarism, we should limit ourselves to "The Waste Land" before Pound worked on it. This version of the poem is easily available for the manuscript has survived. An edition of this manuscript was published in 1974 as The Waste Land: A Facsimile and Transcript of the Original Drafts Including the Annotations of Ezra Pound, and the manuscript itself can be viewed at the British Library. (Here is an online copy.) I don't see any evidence that the advocates of this theory worked from this version of the poem, instead of the later final draft.

And by ignoring these two points, those who argue for Eliot's plagiarism weaken their case with poor scholarship.