By Brett Lock
It is quite right that Transport for London, with the support of mayor Boris Johnson, have pulled the advertising of a so-called "ex-gay" Christian group from display on the London Underground. This group - The Core Issues Trust - now believes its "free speech" is being denied. They are mistaken. Were it, I'd be one of the first to defend their rights.
I am, personally, something of a free-speech fundamentalist. I do not believe there should be legal limits on free-speech other than on occasions where, unequivocally, it is an incitement to violence and intended to intimidate. Why, you may ask, is this not an arbitrary restriction? It isn't. Incitement which seeks to threaten is anathema to free speech.
The freedom to speak freely is important because it facilitates the open exchange of ideas. Intimidating speech is not the expression of a point of view so much as an attempt to stop unwanted points of view from being expressed by others.
Still, too many people are confused about what "free speech" actually means. Some even believe that being criticised for making a statement is an attack on one's free speech. It certainly is not. The marketplace of ideas is rough-and-tumble.
All "free speech" means is that the state will not proscribe free expression. It does not imply that there is a positive obligation on other parties (including the state, or public or private bodies) to facilitate your speech or expression.
In a society in which a fundamental view of free speech were upheld, you would be able to say what you liked from your own stage, publish what you liked on your own press or websites, sell your own books in your own shop, or distribute your leaflets without fear that you might be arrested or your material destroyed.
It does not, however, mean that other parties have to help you, host you, print you or even listen to you.
Let us take for example a group who believes that intelligence is racially determined. They might even be supported by crank scientists who subscribe to this view. Should they be arrested? Should their books and essays be burned? Of course not.
Similarly, there are groups who subscribe to anti-Semitic conspiracy theories. Should their books - such as The Elders of the Protocols of Zion - be banned, their meetings broken up and their spokespeople jailed? Of course not.
Free societies counter speech - even hate-speech - with more speech.
They counter lies with truth. But should Amazon or Waterstones be forced to stock the books published by these groups? Should the BBC be forced to give them airtime? Should theatres be forced to rent them auditoria for their rallies? No. Nor should London Underground have to give them advertising space.
To make it clear: your right to free speech does not imply a positive duty on third parties to facilitate that speech.
Most reasonable people instinctively understand this. They would be horrified if racist billboards went up on the Underground stating as scientific "fact" that black people were intellectually deficient or that were treated to images seemingly out of Der Sturmer while ascending the escalators.
They would have no trouble understanding that the TfL management exercised its right to discretion when selecting which adverts it is willing to display.
In no way does this limit the right of the Core Issues Trust to air its equally poisonous views - which it is entitled to - under its own steam. That entitlement, sadly for them, does not extend to co-opting other parties into helping them spread their views.
But the issue goes beyond free speech. There is another reason why these "ex-gay" adverts ought not to be displayed.
Suppose there were an unscientific 'remedy' for a certain medical condition which had been shown, in peer-reviewed scientific and medical journals not only to be ineffective but moreover to be damaging to people's health. Why on earth would any responsible body agree to give such a product the respectability of mainstream advertising space?
What if it were worse than that? What if the advertising message of the quack-medicine targeted hypochondriacs - people who were not even actually ill?
This is almost precisely what this "ex-gay therapy" does.
For a start, it is not even driven by science. It is driven by religious dogma (though occasionally given a pseudo-scientific veneer, much like homeopathy).
Not only has it been almost half a century since psychiatry last considered homosexuality a "disorder" but for decades all reputable practitioners have held that attempts to change a person's fundamental sexual orientation are damaging and almost always likely to fail.
There will always be cranks with ideas driven by religious zealotry impervious to sense and evidence. I do not propose they are arrested.
I do not demand that their websites are shut down or their books banned, but equally I can't see any reason why a venue should have to rent them halls, or an ISP be compelled to host their website, or a printing works forced to run their books off its presses.
Their predecessors in groups like the True Freedom Trust and Courage UK had an easier time. In past decades, lesbian and gay people were more likely to feel isolated, marginalised and full of shame. It was much easier for these groups to target the confused and conflicted.
But even then "success" as it was proved so illusive that Courage UK gave up and admitted failure. It is now a gay-affirming ministry.
Today, with millions of averagely happy and well-adjusted gay and lesbian people in Britain, the Core Issues Trust must be one of the last hold-outs for this religious-inspired gobbledygook.
With reputable science, medicine and psychiatry contradicting them, the dismal track record of similar "ex-gay" projects, and the life experience of millions as testimony to their error, they're in a desperate corner and understandably frustrated.
Nevertheless, the Core Issues Trust must accept that few will want to facilitate the dissemination of their bizarre ideas, even though they're perfectly entitled to hold them. But their freedom of speech is intact.
Brett Lock is a campaigner with the gay rights group, OutRage!
The opinions in politics.co.uk's Comment and Analysis section are those of the author and are no reflection of the views of the website or its owners.