According to Kant, prostitution is morally wrong. The second formulation of the categorical imperative states that one should never use themselves, or another as a mere means. 1. I can see how prostitution would fail to respect self, as it is using one's body as a "mere means" to earn money. But how is that different from a farmer, who use his body to work in the fields to harvest crops for food and money? 2. Prostitution also fails to respect another, by using the person to satisfy his sexual urges. However, by paying the prostitute, isn't it also respecting her by recognizing her dignity and worth and paying her for her "work"? On the basis of these 2 points, can you please explain why prostitution is morally wrong?

I'm not sure that most contemporary Kantian moral philosophers agree with Kant on the morality of prostitution. As you note, prostitution does not seem to make use of one's own humanity in a way that's fundamentally different from other forms of work or labor which are clearly morally permissible. Why think that prostitution, unlike farming, involves the wrongful use of ourselves merely as a means?

Much of the reason is that Kant was deeply skeptical about the compatibility of sexual desire with the moral requirement to treat rational agents as ends in themselves rather than merely as a means. He writes: “Sexual union is the reciprocal use that one human beings makes of the sexual organs and capacities of another” for the purpose of enjoyment. As Kant saw it, sexual desire is not a desire for a person's good but for the use of their body for one's own physical pleasure. Hence, sexual desire is fundamentally at odds with respect for others' rational natures. Sex is animalistic in that we treat ourselves (and others) as animal-like:

"When a man wishes to satisfy his desire, a woman hers, they stimulate each other’s desires; their inclinations meet, but their object is not human nature but sex, and each of them dishonors the human nature of the other. They make of humanity an instrument for the satisfaction of their lusts and inclinations, and dishonor it by placing it on a level with animal nature."

For Kant, objectification is therefore built into the nature of sex. Sex invariably involves seeing oneself and one's sex partner merely as means. There is a way for sex to be mutually respectful, according to Kant, namely, through marital monogamy. (I won't go into the complicated dynamics of how Kant thought marital monogamy makes sex morally innocuous.) But Kant's opposition to prostitution stems from the contention that sex as such treats the partners merely as means.

Needless to say, Kant's view of the nature of sex is open to question. He seems to think that sexual desire is by its nature an uncontrollable impulse that can't be tamed by reason and is thus inescapably a form of objectification. What I suspect Kant misses is that some measure of objectification may nevertheless be compatible with respect for rational agency. There is certainly a sense in which prostitutes, by commodifying their bodies, are treating their bodies as means (so too are their customers treating prostitutes' bodies as means). But when such a transaction is consensual, non-coercive, etc., one might think that this 'objectification' takes place against a background of respect for one's own rational agency and that of others. (Note that Kantians are likely to find non-consensual, coerced, exploitative sexual activity to be particularly objectionable; sadly, prostitution all too often falls into that category.)

So in the end, it's not clear that Kant's case for the immortality of prostitution is that compelling. It rests on peculiar views about the nature of sexual desire and its compatibility with respect for rational agency that even Kantians might well reject.

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