Last night I debated gay marriage with Peter Tatchell at King’s College London. My opening comments are published below.

There are many reasons to be sceptical of the campaign for gay marriage, this movement that depicts itself as the reincarnation of Martin Luther King yet is only effusively backed by such superbly unradical people as David Cameron, The Times and Goldman Sachs.

But there’s one reason to be sceptical that doesn’t get nearly enough coverage or consideration in my view. And that is the fact that gay marriage will be bad for gay people.

It seems pretty clear to me that this campaign is at least partly born of a very sad and very profound sense of defensiveness in the modern gay movement.

It speaks to a desire among gay rights activists to win external approval for their loves and lifestyles, especially the approval of the state and the moral majority, which they were never interested in winning in the past.

So gay marriage is fundamentally a con, I think. It comes swaddled in pseudo-swagger, with some campaigners even claiming it represents the glorious endpoint to the 1969 Stonewall riot and 40 years of streetfighting for gay rights. But that phoney swagger disguises the defensiveness and neediness and small-mindedness of the gay rights lobbyists driving this campaign.

I think it is informative to look at two areas where there has been a massive about-face in gay politics. The first area is the gay movement’s attitude towards biology; and the second is the gay movement’s attitude towards the state.

On biology: One of the most striking claims made by modern gay activists is that homosexuality is genetic. There is a neverending hunt for the “gay gene”, and scientists and gay campaigners often talk about “gay animals”, too - penguins or sheep that shag members of their own sex, which apparently proves that homosexuality is just a biological thing. In the inane words of Lady Gaga, gays are “born this way”.

This is the polar opposite of what gay radicals argued in the past. In fact, in the past it was anti-gay moralists and Christian campaigners who insisted that gayness was biological. Like the 1950s British theologian who said homosexuality was an “inherent condition” with “biological, psychological or genetic causes”. Some twentieth-century moralists talked about a “gay germ”.

Early gay radicals argued against such biological determinism, claiming instead that their sexual pursuits were a lifestyle not a condition, and one which they had every moral right to choose and enjoy.

Now, sadly, gay activists are rehabilitating the old anti-gay lobby’s biological determinism - though they talk of a “gay gene” rather than a “gay germ”. The gay movement’s retreat from morality to biology speaks to a serious lack of confidence.

Aligned with this is the gay movement’s changing attitude towards the state and towards social institutions. The campaign for gay marriage shows there has been a huge turnaround here, too.

In the past, gay radicals wanted to wriggle free from social institutions, particularly from the insistence that everyone should enter into marriage and live in nuclear families.

The Gay Liberation Front that emerged from the Stonewall riot wanted to smash “all existing social institutions”, including marriage. Early gay manifestos in the 1970s railed against marriage and the family, describing them as “prisons” and “oppressive”.

The demand was for the right to life outside of such institutions; for the liberty to fashion new ways of living that did not require the blessing of the state or the approval of the moral majority.

Now, in a total turnaround, through the gay marriage campaign gay activists are pleading for state recognition of their lives and choices.

If you look at the reasons campaigners give for why they want marriage, it is very interesting - they talk about feeling undervalued, about not feeling complete, about wanting to be welcomed into the “family of state-sanctioned human relationships”, as one writer puts it. This is clearly driven by a feeling of a lack of legitimacy, by a niggling, almost existential doubt and discomfort, rather than by any 1960s-style confidence to demand change.

So, where gay activists once rejected scientific explanations for homosexuality, and declared that they didn’t need a state licence for their lives, now they embrace biological determinism and crave state flattery.

Where once gays and gay activists derived their moral authority simply from their desire to be free, to live how they wanted to live, now they seek to prop up their lifestyles with the authority of science and the authority of the state.

I think this is very sad. It is terrible that the acceptability of gayness is being made contingent upon the authority of science and the state. What happens if either of those changeable entities decides to pull the rug from under the legitimation of homosexuality? What if scientists all decree that there is no gay gene (which of course there isn’t) - would that mean gayness is bad because it is not genetically determined? What if a future government decides that homosexuality falls outside of the “family of state-sanctioned human relationships”? Would that mean gayness is unacceptable?

This is not a complaint about how respectable or bourgeois gay radicals have become. Every radical has the right to put their feet up later in life and to campaign around popular, conformist issues for a change - even Peter Tatchell. Being out on a limb is alienating and sometimes dangerous.

Also, there is nothing radical about being gay. Lots of gays are really boring and conservative.

No, I am not criticising gay campaigners for wanting to be bourgeois but rather am interrogating what lies behind the rather sad need for external approval and recognition. It is not the gay rights movement’s desire to be mainstream and bland that is alarming; most political activists are mainstream and bland today.

Rather, the alarming thing is how they are making homosexuality reliant upon the expertise of scientists and the favour of the state; it’s the neediness for third-party validation that is worrying, not the conformity.

I think this reveals what a trap the politics of identity can be. When gay activists were motivated by the politics of liberation, their demand was for the state to leave them alone. Now that they are driven by the politics of identity, they ask the state to come into their lives and confer its blessings upon them.

The politics of identity, being built upon self-doubt and defensiveness, is an insatiable beast, requiring constant recognition from without one’s own life and community.

Gay rights campaigners now seek that recognition from the realms of pseudoscience and state favour.

So the gay marriage campaign is dishonest - it presents itself as daring and edgy, when in truth it is implicity communicating the message that it is only acceptable to live in relationships that are biologically logical and state-approved. It eats away at the inner logic of relationships, and at the confidence of individuals to formulate relationships that suit them and their lives and their situations.

All of this doesn’t just impact on gays. In granting the state the authority to redefine marriage, effectively to say which human relationships are good and valid, the modern gay movement is helping to boost the authority of the state over all intimate relationships and lifestyle choices.

It is helping to make the state the arbiter of what is acceptable in the arena of love and home and family life.

This is the great tragedy of the modern gay movement - it started out challenging the moral authority of the state over people’s intimate lives, but it has ended up helping to rehabilitate and expand the moral authority of the state in that arena of human existence.

This is an edited version of a speech I gave at King’s College London on 26 February 2013.