How does Fitzgerald use the characters of Tom and Wilson to criticise American Society in the 1920's?

In The Great Gatsby, Wilson is at the
bottom of the social and economic system and Tom is at the
top. 

One specific story line accurately demonstrates
this.  Wilson needs to buy Tom's car so he can resell it and earn money.  That's one
thing Wilson does to earn a living:  buy and sell cars.  Yet, when,
as well as if, this business transaction occurs is completely in the power of the
haves (Tom), rather than the have nots
(Wilson).  The man with the car possesses the power.  Apparently, the
discussion or negotiation concerning the car has been going on for some time.  Wilson
needs the deal to happen quickly, but Tom is taking his time.  When Wilson asks about
the car, Tom gets upset and says that maybe we should just forget the deal, then.  Tom
has all the leverage.  Wilson is at his mercy. 

Wilson is
the one who works even when he's sick so that he won't miss a sale, but Tom is the one
with all the power.       

Other aspects  of humankind are
ridiculed in addition to the social and economic, however.  One aspect of humanity that
serves as an equalizer in the novel is the foolishness of both Wilson and Tom.  In other
words, both Wilson and Tom are fools. 

Wilson is jerked
around by Tom, cuckholded by Tom, fooled by his wife, and, at least in part, suckered
into killing Gatsby by Tom.

Tom is as ignorant of Daisy's
affair as Wilson is of Myrtle's, he latches on to cliche, tired, irrational arguments
concerning race, etc., he rashly judges people and situations based on his own needs and
point of view, and he thinks he is always right.

Thus, both
public and private aspects of the Jazz Age are ridiculed in the
novel.

One shouldn't, of course, however, make the mistake
of assuming the novel only applies to the Jazz Age.  The novels criticism applies to us
and our age as well.