Among the letters was this one from Ethel Tolbach of New York:
TO THE EDITOR: After adolescence, this is no time when modern poetry cannot be seen for the fraud it is. Recently a friend told me that William Carlos Williams was an exception. To my horror I found his poetry full of anti-democratic ideas, anti-Semitism, anti-Negro sentiments--the very symptoms of the virus of "modernism" which Mr. Shapiro discusses.*
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I'm guessing that the charge of anti-Semitism is guilt by association with Pound, an infection spread by the "disease" (Shapiro's word) of modernism.
The odd double negative of the first sentence of this letter is of interest. It befits the antimodernist laments of the period 1945-60: concerns raised about modernism's pernicious influence are said to be urgent, but no alternative (except typically a return to what poetically there was before) is offered. So we don't say that 1960 is a time when we should do such-and-such new or different in poetry. We say it's not a time when we should not disclose failures and betrayals.
* NYT, Jan 10, 1960, p. 32.