What's the smallest unit of celebration? A whooplet? I need one to mark the news that sentencing for drug offences, in some cases, will be shortened. Following new guidelines from the sentencing council from the end of February those found to have bought drugs to share with friends rather than to profit from them, and those found to have imported drugs under duress, can expect to be locked up slightly less often, and for slightly less long. One whooplet, certainly, is the council's to share.

I do hope the grudging tone comes across however: giving a year and a half of prison time to a clubber who bought 20 ecstasy pills and split them with a friend (the guideline "starting point" the council recommends) remains an act of stupidity. In all but the most minuscule number of cases, those pills would have done nothing more harmful than inflict some loss of sleep.

What is welcome, though, is that the new guidelines go some way to recognising the variety of behaviour that constitutes "dealing" or "trafficking". Those words have grim associations they often don't deserve. For instance, it's rather difficult for six friends to buy the exact amount of cocaine, in advance, that each of them wants to take that evening. So they usually split some, which means that at least one of them ends up being a "supplier". I don't know if it's ever been tested in court, but wouldn't even passing a joint around a room constitute a series of acts of "supply"?

Drug "mules", who carry small-to-medium-sized quantities of something through an airport in their luggage (or sometimes in their stomach), have often been coerced into doing so, and this is now rightly being seen as a mitigating factor too. So is low purity – a very knotty problem. Which is the greater crime? Selling a large quantity of diluted cocaine powder, or a small quantity of pure cocaine? And if it's been diluted, what was it diluted with? And did whoever sold it know? Mephedrone became so popular at one time that – even while it was still legal – quantities of it were being cut with other illegal substances. Some people were dealing drugs, in other words, without realising it.

"Drug offending has to be taken seriously," Lord Justice Hughes, the council's deputy chairman explains. "Drug abuse underlies a huge volume of acquisitive and violent crime and dealing can blight communities." But people don't commit crimes because they're on drugs – they commit them because they want money to buy drugs. You might as well say that nice houses blight communities just because some people commit crimes to pay for them.

Britain is not a police state. For the most part, it's a fair and decently run country. Yet our drug policy is like some import from a totalitarian regime. The risks associated with drug use remind me of that trusty threat of "foreign terrorists" dictators use to consolidate their power.

The Conservative MP Priti Patel told the Daily Mail: "These people are not just dealing drugs – they are destroying people's lives." Patel should have a word with some of her colleagues. Louise Mensch admits that it is "highly probable" she took drugs in the 1990s, and she's done all right. Or perhaps it is the tragic case of Barack Obama that Patel has in mind? As a teenager, he made the fatal error of experimenting with marijuana, which led on to cocaine and then – with sad inevitability – to a legal career, and the presidency of his nation.

To be fair to Patel, if you don't take this "destroying lives" line, you'll be forever labelled "soft on drugs" (as even the sentencing council are in the Mail). "Drugs are illegal because they are harmful – they destroy lives and cause untold misery," said a Home Office statement in response to demands for decriminalisation from a group including three chief constables and a former drugs minister last year.

Poor Ed Miliband could only agree, using another favourite formulation. "I worry about the effects on young people," he said, "the message that we would be sending out." When a politician says their policy is based on "sending out a message" you can be sure that what they really mean is that it's wrong, but politically necessary.

Which, of course, has always been the problem with drugs. There are risks associated with their use; but there are very serious risks associated with alcohol, serving in the army or eating badly that we accept. And when the former government adviser Professor David Nutt, pointed out – accurately, in a scientific paper – that alcohol and tobacco were in many ways more harmful than LSD or ecstasy, he was sacked by Alan Johnson because his comments might "damage efforts to give the public clear messages about the dangers of drugs".

As a country, we look back in horror now at the delusions of other eras – when it was illegal to be gay, for instance, or when women could not vote. Yet we do not stop and see that we are living through another one. Decriminalisation would end the violent illegal drug trade; drug treatment and prescription for addicts would prevent them from committing crime. Both measures would make gigantic savings on the cost of policing and imprisoning offenders, and on clearing up the consequences of their actions. They would also end the outrage of people being locked up for the crime of seeking mostly harmless fun. It's our laws that are destroying lives.

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