And mark in every face I meet
Marks of weakness, marks of woe.
In every cry of every man,
In every Infant's cry of fear,
In every voice: in every ban,
The mind-forged manacles I hear.
How the Chimney-sweeper's cry
Every blackning church appalls;
And the hapless Soldier's sigh
Runs in blood down Palace walls.
But most thro' midnight streets I hear
How the youthful Harlot's curse
Blasts the new-born Infant's tear,
And blights with plagues the Marriage hearse.

The harlot’s curse from the line before even sullies the cry of the innocent. Babies born to syphilitic mothers (who had been infected by husbands who frequented brothels) had painful seeping eyes. Of course, new born babies cry, but Blake is suggesting that even this is connected to the oppression endured by those living in London— through syphilis and sexually transmitted diseases that found their way into the “marriage hearse”, connecting the sex trade to the bonds of wedlock and childhood.
London