What is the theme of the poem "The Whorehouse in a Calcutta Street," written by Jayanta Mahapatra?

The most significant theme of this poem, I think, has to do with its depiction of sex workers as individuals with identities that exist outside of the work that they do. There is a temptation for those who visit brothels to think of the women who work there as existing only for their pleasure, as though these women simply wait, naked and willing, for them to arrive so that they can come to life. The speaker seems to mimic, even mock, these thoughts in the first few lines:

Walk right in. It is yours.Where the house smiles wryly into the lighted street. Think of the women you wished to know and haven't.

However, the speaker points out the "secret moonlight of the women" and the fact that their conversation with clients is "false chatter" because they are really thinking of their children, their homes, and their own lives rather than the sexual pleasure they will provide for the men who pay them. The women may feign pleasure, but they are really concerned with other, more mundane, things. These men "miss them in the house's dark spaces" and fail to see these women as individuals, as people with dignity and hope. This is perhaps symbolized by "the far edge of the rainbow" that they feel "faint[ly]" in the centers of their beings.

In "The Whorehouse in a Calcutta Street" Mahapatra challenges the dominant notion in society, which sees prostitutes as somehow subhuman. Mahapatra wants us to realize that, although the women portrayed in the poem may be society's outcasts, they're still human beings, with all the same hopes, dreams, fears, and emotions as anyone else.
The prevailing double standard permits men to seek sexual pleasure with prostitutes but damns prostitutes for providing that pleasure. Those men who cross the threshold of the bordello are only thinking of themselves and their needs; they don't stop to consider that most of the prostitutes they visit are mothers, eager to return home and be with their children. Indeed, the women who work at the brothel are only able to give pleasure to the men precisely because they have left their families at home to go out to work.
In portraying women who sell themselves as living, breathing human beings, Mahapatra is generating an alternative narrative to the one created by society, which licenses men to treat prostitutes as nothing more than pleasure-givers.