It seems to be the ultimate sting. A tabloid newspaper pays a couple of male prostitutes for their story about their time with a senior politician.

Keith Vaz – a senior figure in the Labour Party and one of the best-known Asian MPs in the UK – faced fierce pressure to resign from his key role as chair of the home affairs committee of the House of Commons. In an astonishing display of chutzpah (or bravery, depending on your point of view) he appeared in the Commons yesterday and asked a couple of questions which were greeted with stony silence.

Eventually the pressure became too great. He has just announced he's stepping down.

But that is not all there is to say about this story.

One of Vaz' defenders was Peter Tatchell. He put out a press release which was picked up by several newspapers. Tatchell is someone I have met and debated with. I regard him as a committed, sincere, and honest human being. However, his comments were deeply disappointing: This is what he said about the Vaz case:

"I find it very difficult to see any public interest justification for the exposure of Keith Vaz. He may have behaved unwisely, but there is no evidence of criminal wrong-doing or hypocrisy.

"Buying sex is not an offence. Keith has supported gay rights and the decriminalisation of sex work. His public pronouncements do not contradict his private behaviour.

"So where is the public interest in outing him?

"Given the absence of any public interest justification, there is prima facie evidence that the Sunday Mirror has broken the press regulation code prohibiting unwarranted intrusion into privacy.

"It is true that that Keith did not declare an interest when his Home Affairs Committee was investigating poppers and sex work criminalisation. But we don't demand that MPs who drink and smoke declare an interest when they discuss legislation affecting the alcohol and cigarette industries. Why should Vaz be treated any differently?

"We must be mindful of how hard it is for gay and bisexual people to come out in some sections of the Asian community, where conservative, traditional views often hold sway. Homophobia kept Keith Vaz in the closet and we should all be appalled by that."

So what's wrong with all of this?

Peter Tatchell's political ideology and sexual philosophy is blinding him to the irrationality of what he is saying. Keith Vaz is chairman of a committee which is responsible for looking into issues such as prostitution and drug abuse. As Joan Smith in The Guardian argues: "To put it bluntly, he appears to have chaired hearings where campaigners proposed a change in the law that could, in theory, turn his own private behaviour into a criminal offence. This is jaw-dropping stuff, and it's hard to think of a more blatant conflict of interest.".

Of course, if the allegations are true, he is a complete hypocrite. There is a great deal of public interest justification in having a senior politician chairing a committee which is looking into prostitution and drug abuse, when he himself is alleged to have taken part in both. Tatchell's commitment to his own political sexual ideology seems to override any common sense and any sense of justice. In fact his public statement seems to want to turn Keith Vaz into some kind of gay hero, a victim of homophobic abuse especially from the Asian community.

But if you stop to think, you realise how absurd Tatchell's position is. He objects to the newspaper buying the men's story but has no objection to Vaz buying their bodies. The two young men who were allegedly hired by Vaz are Romanian immigrants. Does anyone honestly think that they were 'consenting adults' who would have been there without the money? This is a classic case of the rich exploiting the poor.

Should Sex be Sold?

There is a much wider issue here, namely the question of selling sex and the subsequent sex slavery that follows. There is a debate going on in Western society just now about this issue. On the one hand the more progressive countries like Sweden (and Northern Ireland) have adopted a model of criminalising the buying of sex, so that the buyers rather than the prostitutes are held responsible. On the other hand there are those like Tatchell who want prostitution to be legalised. The BBC and others in the main stream media are buying into and acquiescing in this when they talk about prostitutes as being 'sex workers', and prostitution as 'the sex industry'. It's not work and it's not an industry. It is a system of abuse which leads to the exploitation of the young and the poor at the expense of the old and the rich.

It is absolutely hypocritical of Parliament to have as the head of its committee on Home Affairs a man whose activities encourage prostitution and the slave trade that inevitably follows from that. It is estimated that there are more than 20,000 sex slaves in the UK today. Sex trafficking is a serious problem. And yet a 'social justice' campaigner like Tatchell is more worried that this is either a result of, or could lead to, homophobia, than he is about those who are sexually exploited by the rich and powerful. What kind of society are we creating where this kind of behaviour is tolerated and defended, even among our senior leaders?

This morning I read this in St Augustine: "The knowledge of anyone is not conveyed to us in his bodily countenance, but only lies open to our apprehension when his life and character are revealed" (Tract 15, on John 15:23).

In a more just and fair world we would not judge politicians by the colour of their skin, the size of their bank balance or the skill of their plastic surgeon, but rather by their character: how they keep their vows, how they deal with other people and how they conduct their business. It's funny how Martin Luther King's great quote is now despised by many of our elite commentators. King said: "I have a dream that my four little children will one day live in a nation where they will not be judged by the colour of their skin, but by the content of their character." Now we are told that we must not question character.

If a man takes an oath to be faithful to his wife and then betrays her and his children with prostitutes, is that not relevant to what their character is, and how they will govern? Can we seriously contemplate having a man who allegedly uses prostitutes and drugs being responsible for the body that makes the laws that govern these activities? To anyone with any sense of justice it is a surreal idea. And yet such as been the degradation of our society, as it has removed itself from its Christian roots, that some of today's politicians and today's papers are arguing just that. It's a private matter and is none of our business.

Theresa May is certainly correct in saying that the public must have confidence in our politicians, but wrong in saying that "what Keith does is for Keith". No: if what he does involves buying other people then it is not just for Keith. Equally Jeremy Corbyn is certainly wrong (and living in a fantasy world) if he thinks that Vaz' behaviour is a "private matter". Today the headlines are not about Vaz, but about Sports Direct giving their workers better contracts. There is a sad irony here. Mr Corbyn will rightly complain about the injustice of the exploitation of the Sports Direct workers, and yet he seems to regard the exploitation of Romanian immigrants as a "private matter" because it involves sex.

If our politicians really want to deal with the issue of slavery and trafficking then they need to criminalise the purchase of sex, just as we have criminalised the purchase of heroine and the purchase of guns. If, for the sake of their messed up and confused post-1960's sexual ideology, they refuse to do so, then they are participating in the real perversion of justice and of humanity. The definition of evil favoured by liberal secularist atheists is "that which causes harm". There is no doubt that selling sex causes a great deal of harm.

Who is going to stand up against this evil? Who is going to move away from the platitudes about privacy and ask that our leaders hold to basic standards of common decency? I wonder how many will have the guts and the integrity to stand for justice and real social equality – or will they continue to create a world where everything from votes to bodies, is for sale to the highest bidder? Do they really want to create that unequal, unjust and exploitative society?

David Robertson is the moderator of the Free Church of Scotland and director of Solas CPC, Dundee. Follow him on Twitter @theweeflea.