This is a man-made solitude, A sign of human scheme gone wrong, Wherein weak men are put to brood Until their hatreds make them strong.
This is a monument to shame, In which man hides his social ills; Reluctant, he, to share the blame, When have-not heart its revolt spills.
This is a sinister silence, Which mocks the hopes of they who wait. Ah, what a huge, wasteful expense, To fashion factories that make hate!
Standing before a prison, the speaker doesn't see justice at work. He sees a failure. Each stanza opens with the same flat "This is," as if he's pointing at the building and naming what it really is: a "man-made solitude," a "monument to shame," a "sinister silence." The repetition gives the poem the feel of a verdict being handed down, not on the inmates, but on the society that locked them away.
The speaker's anger is aimed at the system, not just the people inside it. Prisons, he argues, hide "social ills" instead of fixing them, and the line about the "have-not heart" suggests that poverty and exclusion help drive the very crimes being punished. Men sent there to "brood" come out stronger only in their hatred.
The final couplet lands the bitterest point: prisons are "factories that make hate," an enormous and wasteful expense. The mood is cold, grim, and quietly furious.