I wouldn't be surprised if that juror has heard sermons in which that very line of reasoning was used. It was even used by Wordsworth—yes, the same guy who was enraptured by daffodils:

From Sonnets upon the Punishment of Death by William Wordsworth, 1840:

II.

Tenderly do we feel by Nature's law
For worst offenders: though the heart will heave
With indignation, deeply moved we grieve,
In after thought, for him who stood in awe
Neither of God nor man, and only saw,
Lost wretch, a horrible device enthroned
On proud temptations, till the victim groaned
Under the steel his hand had dared to draw.
But oh! restrain compassion, if its course
As oft befalls, prevent or turn aside
Judgments and aims and acts whose higher source
Is sympathy with the unforewarned, who died
Blameless,—with them that shuddered o'er his grave,
And all who from the law firm safety crave.

XII.

See the Condemned alone within his cell
And prostrate at some moment when remorse
Stings to the quick, and, with resistless force,
Assaults the pride she strove in vain to quell.
Then mark him, him who could so long rebel,
The crime confessed, a kneeling Penitent
Before the Altar, where the Sacrament
Softens his heart, till from his eyes outwell
Tears of salvation. Welcome death! while Heaven
Does in this change exceedingly rejoice;
While yet the solemn heed the State hath given
Helps him to meet the last Tribunal's voice
In faith, which fresh offices, were he cast
On old temptations, might for ever blast.