Last month, Amnesty International’s decision-making body meeting in Dublin voted ‘to adopt a policy that seeks attainment of the highest possible protection of the human rights of sex workers, through measures that include the decriminalisation of sex work’. The policy rests ‘on the human rights principle that consensual sexual conduct between adults is entitled to protection from state interference’.

All the following statements are true. Some women are trafficked into prostitution and have no say in it. Others become prostitutes because of material need or childhood trauma. Most but not all prostitution is offered by women and girls to male customers. Many female prostitutes are under the control of violent or otherwise coercive pimps. Collateral problems, including drug abuse and HIV infection, can result from it or (in the case of drug addiction) promote it. Some people, including some women, prostitute themselves because they prefer it to other ways of earning money. There is no reason to think that any measure, whether for producers, consumers or both, including outlawing or criminalising it, will put an end to it, and even the balance of probabilities is disputed.

In response to Amnesty’s proposal, a battery of moral big guns, from the pope, Jimmy Carter and the Guardian to Meryl Streep and others on the red carpet, urged that matters are very simple: ban it, and criminalise the punters but not the prostitutes, as Sweden has done. Others strongly oppose the paternalism this might be thought to license. Liberal feminists argue that since each person owns her body, she may decide what to do with it, whether that means evicting unwanted foetuses or renting it for sex. The pope presumably accepts the moral continuity between abortion and prostitution but infers the opposite, by denying the strong ownership premise or by holding that these practices abuse the God-given gift of reproduction. Others invoke strong ownership rights when it comes to abortion, but hit the override button with prostitution: women who engage in it clearly can’t have freely chosen to do so. This is true of some Kantians, who identify freedom with autonomy but (in version two of the categorical imperative) say that you shouldn’t use your own person as a mere means, which prostitution may be thought to do: hence prostitutes are not acting autonomously. Maybe banning it amounts to unwarranted restraint of trade. A wants sex, B wants A’s cash, and – bingo! – the market has worked its magic, though few people think that burglary or crack-pushing, say, are callings that the state must protect. Or, simplest of all, there’s the view that prostitution is just bad, so anything that stops it is (at least to that extent) good.

In the public arena, moral certitude tends to gerrymander supposedly factual claims. Does outlawing prostitution curb sexual violence by pimps and punters, or encourage it? The English Collective of Prostitutes supports Amnesty’s stance, one argument being that customers are more likely to act violently towards prostitutes if they are already engaged in criminal activity. Many feminists say that prostitution either is in itself, or sanctions, sexual violence against women. Others claim that the Swedish law makes prostitutes liable to eviction by landlords fearful of pimping charges, though that could equally go for the English regime which bans living off ‘immoral earnings’. Germany, where brothels are legal, is alternately held up as a magnet for sex tourism and human trafficking, or a liberal oasis where sex workers (even the term is contested) enjoy standing similar to other employees.

Part of Amnesty’s problem is that it deals in human rights, whose strong suit is moral clarity. Tackling fiddly social problems with rights-talk can be like trying to undo a knot with boxing gloves on. This all-or-nothing stance tends to get echoed in the justice-based theorising that dominates political philosophy, where either renting oneself for sex is demanded by justice, and hence a right, or proscribed by it, and so the object of a negative duty. In this setting Amnesty risks getting beaten to the punch by big names with strong opinions for export to social media. Human beings are complicated beasts who perform their animal functions in diverse ways. Dealing with their ramifications is, accordingly, a complex political business. It calls for various things – careful research rather than a priori sociology, an awareness of complexity, a willingness to weigh the prophylactic and other interests involved, and an ability to keep one’s nerve in the face of distraction. But moral foghorns aren’t among them.