How can The Metamorphosis be viewed as a socially critical novella?
The very creative Oscar Wilde keenly observed, "Most people's thoughts are quotations," and, indeed, many have borrowed from the ideas of the minds of philosophers, profound thinkers, social reformers, satirists, and introspective and observant writers. In a sense, the mass of men are much like the family of Gregor Samsa in their complacency to allow others to think for them. This resulting mental indolence allows others, such as politicos, to conspire against them, deluding them with "conventional wisdom" and euphemistic expressions that cloak their exigent desires. In The Metapmorphosis, it is only after the three boarders, who come from the outside,witness and feel revulsion for the metaphoric vermin that Gregor has become because of his family's indolence and exploitation of him, that the family feels "we must get rid of him."
In another parallel to the increasingly socialistic societies of contemporary times, there are those who allow other members to do all the work for the others. Indeed, there are parallels in which certain able-bodied individuals--like Gregor's father and sister--weakly and indolently prefer to live off the efforts of hard-working people, who are forced to not only support themselves, but to enable those others who are capable of working but do not because they can live without effort, profiting from government programs which increase the taxation of those who work.
Certainly the novel can viewed through a Marxist lens. Gregor lives to work, as is obvious by his first thoughts which are occupied by his anxiety of being late to work. This is followed by a visit from the chief clerk, so quickly arriving to demand his excuse. You see, the machine of capitalism requires Gregor's appearance.
It's also interesting to note, that though the family is certainly not wealthy, they are able to afford help. In the end, it is the maid who discovers Gregor's corpse and tosses Gregor into the trash, a nice comment on the duties of social class - the upper classes effectively washing their hands of the lower class, i.e. Gregor. And for protecting the family from the truth of their immorality, their lack of familial duty to Gregor, she will be fired. The family desires upward mobility and cannot cling to the socially unacceptable appearance of the vermin or anyone who can link them with that history.
It's also interesting to note that on the train ride after Gregor's death, the mother and father have high hopes of Grete getting married, fulfilling the social construct of female oppression. One would think that Grete is a character in the feminist mold, but her parents traditional values may stifle her own metamorphosis into an independent woman, which seemed to be indicated by earlier events (her new job, her dominance over Gregor, her decision to be rid of Gregor).