Denial is the only fact — Slavery

The key is to find out why it, the denial, is "the spoiler of Our Home." Line five gives the hint, all men are created equal.

Denial－is the only fact ¹
Perceived by the Denied－
Whose Will－a numb significance－
The Day the Heaven died－

And all the Earth strove common round－⁵
Without Delight, or Beam－
What Comfort was it Wisdom－was－
The spoiler of Our Home?

(F.826/J.965)

[1] Denial:: the human right being denied.
[2] the Denied:: slaves, hinted by line three and five.
[3] Whose Will a numb:: slaves whose wills are suppressed.
[4] Heaven died:: the happy land (America) died of slavery.
[5] round:: the vault of heaven _{(OED 1c)}. all the Earth, common round:: all creatures in this land fight for their rights under the common sky.
[6] Without Delight:: slaves in this land are unhappy.
[7] Comfort was it:: comfort of the slavery.
[8] Our Home:: the United States. The spoiler:: this poem was written around 1864, and Civil War was spoiling the country.

Whereas, slavery, or involuntary servitude, except as a punishment for crime, is a violation of the inherent and inalienable rights of men, a crime against justice and humanity, a disturber of the Union and of domestic tranquility, a hindrance to the common defence, a spoiler of the public liberties, has inaugurated civil war, and is the cause of our national calamities; ─ Miscellaneous Documents of the House of Representatives (1865)