Well, of course the Assisted Dying Bill failed. It mattered not a jot that an overwhelming majority of public opinion urged its success; it was always going to fail and the only surprising thing is that anybody is surprised. I’ll bet my teeth on a few more certainties, too. Last week the required 200,000 people put down their spliffs long enough to sign a petition in favour of decriminalising cannabis and thus, in October, the matter will be debated by MPs. Proponents, however, really should not bother — they will lose, regardless.

Also last week it was reported that genetic engineering is now our most rapidly developing area of scientific research; nevertheless, each of its life-enhancing discoveries continues to face immense hurdles — at which many fall — on the journey between laboratories and needy patients. In every case, the chance of change succumbs to the same argument: that of the ubiquitous ‘slippery slope’. Assisted dying bit the dust not because anybody seriously wishes to prolong agony among the terminally ill but because, in the dark minds of scattergun alarmists and conspiracy theorists, to allow it would be a slippery slope towards truckloads of septuagenarians being hurled, still kicking, into the gaping mouths of crematoria.

Lightening up the law on cannabis may be opposed for several reasons, good and bad, worthy of consideration and far-fetched. It does not tax me particularly, either way; I never was greatly fond of the stuff. But when it returns to debate next month, the move will fail not by dint of the reasoned arguments. It will fail because, as always, the ignorant cling to the belief that the use of cannabis is a slippery slope towards the use of, say, heroin — in spite of countless studies proving the exact opposite. If you don’t have to go underground for your weed, you won’t be introduced to the nastier products for sale in the same den — much as, if you do not venture into the high street, you are less likely to indulge in an impulse buy from a shop window.

The massed opposition to genetic engineering must break the cleverest of hearts when they are accused of creating a slippery slope to ‘designer babies’. I cannot imagine how it would feel to have found a way to manipulate a gene in order to save a baby from being born into the lifelong anguish of cystic fibrosis, only to be greeted by an intake of breath: heavens, no! Next thing, women will be asking for children with blue eyes!

Taken simply as a tool of argument, the slippery slope demonstrates a paucity of intellectual rigour: it is one thing to oppose what is being proposed and another altogether to oppose what is not. The first requires knowledge, study and fact; the second needs neither evidence nor proof and is validated as a warning by nothing more than its own utterance.

In efforts to beef up the warnings there are those who cite the experience of other countries, as did Douglas Murray in his cover story a fortnight ago. Douglas cited Holland and Belgium, but what happens in other countries is not an inevitable template for what will happen in this one. As long as there are laws that apply in Dover but not in Calais or Amsterdam, we have only the record in Britain as a credible measure — and in this country, often almost to a fault, we have shown ourselves to be pretty damn rigorous both in finding consensus and in sticking to it.

Sometimes we involve the law. So, for instance, when gay sex between men was made legal in 1967, and the law specified only men over 21, we continued to prosecute younger hanky-panky. In 1994 we returned to Parliament for stout debate and consideration, before reducing the age to 18. For the sake of parity with heterosexuals, we repeated the arduous procedure and, in 2001, 16-year-olds were included. There was no slope, slippery or otherwise — just three clear, controlled and legislated steps.

Speaking of 16-year-olds: we are the only country in Europe that allows military recruitment at 16 rather than at 18. Some of us would like to change that (16 is awfully young to be able to sign away the next six years of your life, including risking it in warfare, to a strictly binding agreement). But none of us would sensibly argue that these 16-year-olds are perched upon a slippery slope leading to 12-year-olds navigating drones over Iraq. Even though, in these techno-years, they would probably make a better fist of it than their elders, we do not teach our children to kill. This is Britain, not Sierra Leone.

Sometimes, we do not need to involve the law; consensus is reached culturally, yet clung to all the same. Most people in this country eat meat — but that does not include chowing down on the family dog or raiding the local gymkhana for Sunday lunch.

And sometimes what begins in law becomes simply absorbed into cultural consensus. We used to speak of ‘legal limits’ for alcohol consumption before driving a car; these days most people unthinkingly recognise that a couple of swift halves after work might be fine while competitive sinking of yards of ale is not — and we don’t think that anyone who defies that principle is either big or clever.

Moreover, when we discover those who have found loopholes and wiggle-room, we have proved ourselves to be collectively cleverer at blocking them than the scaremongers allow. For example, once we established that there were some who were abusing scans during pregnancy to determine the sex of their child, and then terminating those of the ‘wrong’ sex, most NHS hospitals took it upon themselves to inform parents that it was not the hospital’s policy to tell them what sex they were expecting. What they did not do was invoke the slippery slope to stop the scans that have revolutionised antenatal medical practice.

(Of course, as an aside, we must admit that the very rich can still get around that one, as they can get around so much else. Then again, we must also admit that, by and large, it was not the very rich who were guilty of the abuse; it was the poor, the illiterate and — are we allowed to say this? — the non-British.)

Patriotism may be an overrated virtue, but I have faith in the everyday common sense of most of my countrymen and their capacity to understand precisely when and where to apply brakes. As for those who seek only to stifle potential, who cannot embrace any progress, change or evolution without conjuring out of thin air a terrifying slippery slope, we would be better served if they would shut up, suit up and ski down it instead.