Helen Lewis says we need a word for the kind of idea that’s good if used sparingly but otherwise toxic; she suggests “alcopinion.”

In the recent debates about Amnesty International changing its policy on prostitution, we’ve heard a lot of one particular alcopinion: to fight our way through the legal, ethical and safety concerns, the answer is simple – we should ignore everyone else and “listen to sex workers”.

Those pushing this line present the current debate as a straightforward dichotomy: on one side are sex workers, an apparently homogenous group who want decriminalisation of both sides of a sexual transaction.

On the other side are Lena Dunham, Meryl Streep and assorted actresses who signed a letter to Amnesty saying that decriminalising sex buyers was siding with “pimps and other exploiters”.

According to the prevailing tide of internet feminism, it is easy to tell who is right. You simply look at who is speaking.

Except that who is speaking isn’t always the same person, and that means the opinion isn’t always the same either.

But framing the debate this way is absurdly misleading. It conveniently ignores that the Amnesty letter wasn’t only signed by Dunham – she is not the sole arbiter of feminism in 2015, whatever 1,000 overwrought blogs would have you believe. It was also endorsed by charities, academic researchers and those who style themselves as “prostitution survivors”. These are women with direct experience of the sex trade who believe it is intrinsically demeaning and harmful.

Yes but those aren’t the ones you’re supposed to listen to. That’s the problem with  “listen to sex workers” if you’re listening to them in order to choose one policy as opposed to another – you have to figure out which ones.

Unsurprisingly, women who experience prostitution as little more than paid rape will do everything they can to leave the trade. But that means they’re not sex workers any more. So – hey presto – their opinions can be discounted. We end up in a “no true Scotsman” situation that skews the answers we get; only people with an overall positive view are permitted to talk about that industry. It’s as if the Leveson inquiry had only heard from News of the World journalists.

It’s as if only happy pre-cancer smokers could discuss tobacco policy; it’s as if only oil company executives could talk about climate change.

(Ok it’s not really, because the parallel is less than exact, but the stacking of the deck is parallel.)

And then what about former sex workers who don’t want to chat in public about their former sex work? Not everyone does, Lewis points out.

Are those people not allowed to speak? Finally, prostitution is a public policy issue. We all live in a society in which sex is bought and sold and its existence has consequences for all of us. Demanding that the vast majority of us shut up is like telling renters they can have no opinion on the mortgage market or that atheists can’t complain about faith schools.

Or like telling cis women we’re not allowed to talk about gender.