Why do the passengers on the Dover mail act towards each other as they do? A Tale of Two Cities by Charles Dickens

In the opening chapter of the Dickens's historical novel,
A Tale of Two Cities, Dickens creates a tableau of the times: 
Highway robbers are proliferate as "in England, there was scarcely an amount of order
and protection to justify much national boasting."  Robberies and buglaries are nightly
occurrences. Highwaymen, too, abound; so, there is a tremedous distrust and fear that
exists within the hearts of many a Englishman.

Therefore,
in Chapter II of the Book I, the passengers on the Dover Mail, the stagecoach that
carries the mail to the Dover point where it then goes on to Calais, France, are
extremely wary and very suspicious of anyone they do not know.  Dickens writes that
the three passengers, one of whom is Mr. Lorry, have their faces covered with only their
eyes peering out from "many wrappers."

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In those days, travellers were very shy of being
confidential on a short notice, for anybody on the road might be a robber‚ or in league
with robbers.

The coach guard
is extremely cautious as anybody on the road that they traverse may be a robber, or in
league with robbers; in fact, he watches the "arm-chest" that has six or eight loaded
rifles and several cutlasses on top of it.

As the
passengers who "suspected everyone else," mount the hill by walking in the mud next to
the stage, not one ventures ahead for fear that he

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would have put himself in a fair way of getting
shot instantly as a
highwayman.

Being an older
gentleman, Mr. Lorry remains on the step of the coach, half in and half out, but he like
the others looks to the driver to the guard and back again as they continue up the muddy
hill.  When the coach stops, it is as though the beating of their fearful hearts can be
heard, especially when the sound of a horse at a fast gallop is discerned.  When he
detects this sound, the guard calls out, "So-ho!" and threatens to
shoot.

It is Jerry Cruncher who approaches and asks for the
passenger Mr. Lorry, who verifies himself.  But the guard tells Cruncher to approach
slowly,

"And
if you've got holsters to that saddle...don't let me see your hand go high 'em.  For I'm
a devil at a quick mistake, and when I make one it takes the form of
Lead."

At this point Mr.
Lorry calls out to the guard, who has his right hand on the stock of a blunderbuss: 
"There is nothing to apprehend. I belong to Tellso's Bank....I am going to Paris on
business."  When Mr. Lorry returns to the cab, the others have secreted their watches
and purses, pretending now to be asleep.  The coach moves forward, and the guard
replaces his blunderbuss with attention to where is artillery is should he need it
again.