How does Blake portray people in the poem 'London'?

His view of humanity in this poem is, to say the least, bleak and desperate. Blake seeks to provide a portrait of Londoners, particularly members of the lower-class, struggling to survive in the Industrial Age.

The narrator is walking through the streets and regarding the faces of other passersby:

I wander thro' each charter'd street,

Near where the charter'd Thames does flow,

And mark in every face I meet

Marks of weakness, marks of woe.

"Chartered" could indicate private property, or a space (e.g., city, street, school) that has been established. For the purpose of the poem, Blake seems to use the word to remind us that we are in a civilized space, but that civilization has not made us any more humane or content. Perhaps our discontent is rooted in our growing too distant from nature. Notice, too, how the Thames, a natural formation, has also been "charter'd." 

Every face has "marks of weakness" and "woe." The use of the word mark, as both a verb and a noun, indicate that the strangers are stained or sullied. One thinks of marks of soot or oil that one would see on the body of a factory worker.

Though he does not describe any of these strangers, but instead gives us a catalog of types, Blake accounts for the singularity of everyone's anguish:

In every cry of every Man,

In every Infant's cry of fear,

In every voice, in every ban,

The mind-forg'd manacles I hear:

With the use of the adverb "every" he gives distinction where there is otherwise none. The distinction, for humans, lies in the pained sounds they produce. "Ban" has several meanings. It could indicate social and legal prohibitions, public condemnation, or be a play on "banns," which were marriage proclamations. What all of these "bans" have in common is that they are institutional restrictions placed on people -- hence, "mind-forg'd manacles." The narrator hears the clanging of the shackles with which each person has locked down his or her mind in the interest of being a member of society.

The last two stanzas more specifically address people who are representative of political concerns. "The Chimney-sweeper" is a figure about whom Blake had written several poems. Here the chimney sweeper cries, which echoes the "cry of every Man" and "every Infant's cry of fear," but also alludes to the chimney-sweeper advertising his services:

How the Chimney-sweeper's cry

Every blackning Church appalls,

The misery of a boy sweeping out chimneys to live is an outrage or shock to the Church, or should be. Blake's use of the present participle "blackning" suggests a Church that is implicit in this. Churches, too, require the services of chimney-sweeps to clear out soot, which could blacken the space. "Blackning" also suggests guilt or shame for the Church's lack of action on this matter.

The next two lines take issue with the state:

And the hapless Soldier's sigh

Runs in blood down Palace walls.

The soldier is a victim ("hapless") of political maneuvering. He takes his last breath ("sigh") and the reverberations of his death are felt in the palace, for they are guilty -- stained with his blood. There is some alliteration in these lines as well, with the repetition of the "s" sound both at the beginning and end of various words. The effect here is like that of a hush.

The last stanza looks at a prostitute and the effect her desperate actions have had on her child. This is the figure on whom Blake focuses: "But most thro' midnight streets I hear." "Most" indicates that the sound she produces from her "curse" are all too familiar to the narrator. "Curse" has a double-meaning here. It is both profanity and probably venereal disease:

How the youthful Harlot's curse

Blasts the new-born Infant's tear,

And blights with plagues the Marriage hearse.

The blast on "the new-born Infant's tear" indicates that the child is blind. Untreated gonorrhea can have this effect on newborns. Moreover, her ability to spread this disease, and possibly others, to her married customers results in the deaths, both spiritual and possibly literal, of those men's marriages. Untreated syphilis can result in death; and realizing that one's husband has been with a prostitute can destroy the marriage bond. Thus, the marriage coach becomes a "hearse."