What does the poem "Justice Denied in Massachusetts" mean?

Edna St. Vincent Millay writes this poem in response to the Sacco- Vanzetti Trial in 1927.  Millay was concerned with the face that the two Italian immigrants did not receive a fair trial, and were caught up in the national preoccupation with rooting out Communists and Anarchists, known as the "Red Scare."  Sacco and Vanzetti were working class immigrants, accused of robbery and murder.  The trial was quickly undertaken, and there was a scant level of evidence, rather convicting them on the basis of their Anarchist beliefs and their immigrant status.  Millay writes a poem that laments the fate of the two convicted individuals, but also the lack of opposition which spoke out to help Sacco and Vanzetti.  Millay writes of a retreating public. This is not the America asserted voice in "We hold these truths to be self evident," but rather has become an America that says, "Let us abandon then our gardens and go home."  In Millay's mind, the desire to remain withdrawn and disengaged in the affairs of the state caused the miscarriage of justice in the trials of Sacco and Vanzetti.