Stephan's moral values undergo a profound shift as the play develops. You might say that his early moral values--which were diametrically opposed to his father's--were built upon airy castle's of idealism without any foundation in factual experience. This may be said because Stephan begins by rejecting his father, Andrew Undershaft, but once he has gathered some facts to replace his idealist imaginings by actually going to see his father's work and the living quarters of the foundry's employees, he comes to respect and admire his father and the value of the work he does.
Well, to a certain extent, these two characters are juxtaposed in their differences. Stephen, we are told, is a "gravely correct young man" who seems to be burdened by his sense of morality in the way that his opportunistic father definitely is note. Although he shows his strength in the way he plans his future, he is very definitely contrasted to his father in the way that his father is happy to profit by selling arms and weapons and lacks the moral scruples of his son.