When they prosecuted Paula for running a brothel last year they had to resort to a 450-year-old law (the charge called it a "bawdy house"). That says it all, really.

But if you ask Paula who she is really mad at, it isn't the legal ass which convicted her - it's the kind of people who read this newspaper. "There's people who think they're open-minded - people who don't accept racism, don't accept sexism, don't think of themselves as homophobic. They like to think they can accept all walks of life, but they can't. They have an 'ism', a 'prostitute-ism'."

Paula is right. Something strange happens to otherwise democratically-minded people when it comes to sex work. We too have seen this "ism" close-up.

One would have thought it self-evident that the best way to confront exploitation in the sex industry is to empower the women and men who work in it. Change happens when the oppressed themselves say enough is enough. It was black people who confronted racism; gender inequality was fought first and foremost by women; dreadful working conditions by workers selforganising through unions.

Yet when it comes to the sex industry, social reformers become moralists and certain strands of feminism lose the plot. Witness Julie Bindel, writing on these pages recently, who was enraged at the very idea of a sex workers' trade union.

The justification for this position is riddled with contradiction. It usually starts with a description of the misery of prostitutes who face daily victimisation and violence; it concludes that this abuse defines the industry and that allowing prostitutes a union would simply legitimise it. In other words, the greater the exploitation, the less justification there is for a union. What complete nonsense.

But there is something more sinister about this argument: why do these moralists want to portray all sex workers as degraded junkies with lives of unremitting misery? In fact, less than a third of prostitutes are street workers. Of these, not all are drug users, and it is insulting to assume they are. Of those who are, a chaotic lifestyle and drug use usually preceded their sex work and is not (as Bindel suggested) an inevitable consequence of it.

The problem is that in their hearts these concerned moralists regard all sex workers as by definition degraded; people who are somehow no longer capable of social self-determination. They may think they want labour rights, the argument goes, but in fact they are so debased by their circumstances that they don't know what they want. They need to be rescued. This is dangerous and condescending nonsense.

The other plank in the antiunion case is even weaker. The moralists argue that sex work is not work at all, but abuse - and therefore workplace safeguards like unions are not relevant. On what conceivable grounds is it not work? It is certainly an important economic activity. Prostitution generates in excess of £700m a year in Britain. The wider industry, including lap dancing and pornography, earns millions more and employs tens of thousands. For many women around the world sex work is not just work, it is the only available work; for many in this country it is the best of the available options. Better than working shifts in a fish processing factory, say. As one working woman put it: "When I become Jazz (her working name) I like myself better. I get less hassle and less aggro in here [the massage parlour] than I get at home. I get treated with more respect here than I did when I worked in a bar. Here I am liked."

Of course that says much about our society and the contempt in which many workers, and many women, are held. It says a lot about the hardship in Jazz's family life, too. But it also says something about sex work. A lot of sex work is dreadfully exploitative. But not necessarily all of it. The people able to say what is acceptable and what must be challenged are those who work in that industry. It is not up to outsiders to say to Jazz: "OK you can join a union - but only if you leave sex work and get a job in a bar."

Finally, in an attempt to silence sex workers altogether, liberal opponents of the union attempt to dismiss the sex worker activists in the GMB as "not typical". The same could be said of the Tolpuddle Martyrs, but their activism helped improve the lives of "typical" workers.

In the few months since the sex industry branch was formed it has attracted 150 members, and has signed recognition agreements with several table-dancing clubs, where working conditions have improved - codes of conduct and grievance procedures have been introduced, and union reps have been elected. It's a start.

Concerned hand-wringing over the morality of prostitution will neither remove nor reform the industry. And telling sex workers that what they do is so degrading that they are not entitled to a union helps perpetuate the stigma which encourages the violence from which so many sex workers suffer. Whether you like it or not, women such as Paula and Jazz don't want to be saved - they want the right to do their work in a decriminalised industry, they want labour rights and health and safety rights. They want dignity and respect.

· Ana Lopes is a student, a sex worker and spokesperson for the sex workers' branch of the GMB; Callum Macrae is a journalist and filmmaker who directed My Body, My Business.