For any tourist visiting Seattle, there’s the standard bucket list: ride the monorail, ascend the Space Needle, pay a visit to the world’s largest building, and, if you’re not squeamish about tax avoidance, check out the first-ever Starbucks and the Amazon Spheres.

But, as I discovered on a recent visit, there’s a new attraction in town: the cannabis shops peppered through its downtown since Washington state legalised recreational marijuana.

They couldn’t be further from the smoke-filled coffeeshops of Amsterdam: this is very much America does weed. Show your passport at the door and you’re waved into a cheery space filled with brightly lit glass cabinets displaying their wares. Yes, there’s row after row of the little packets of greenish stuff you’d expect, with enticing names such as “Pink Lemonade” and “Chocolope”. But lots of other cannabis-infused goodies too: vape pens, pre-rolled joints and “edibles”, from brownies to jelly sweets to drinks.

Budtenders are on hand to “talk flower” with discerning pot veterans, and chat with canna-curious tourists about the basics, such as the difference between the psychoactive THC, which produces a “mind high”, and the non-psychoactive CBD, which results in a healing “body high”. (Me: “But what’s the difference between a mind and a body high?” Patient budtender: “One makes your mind feel high, the other your body.”)

If the goal of cannabis prohibition was to reduce social harm, it’s been an unalloyed failure

It was fascinating talking to Washingtonians about what they’ve got right and wrong in regulating an industry from scratch. And as I tucked into my first vegan mockburger on the plane home – nicely pink inside, my tastebuds honestly couldn’t distinguish it from the real thing – it left me thinking, why are we so willing to wield the nanny state when it comes to cannabis but not something like meat, which does real social harm?

If the goal of cannabis prohibition was to reduce social harm, it’s been an unalloyed failure. As even President Obama admitted, it’s safer than alcohol: it’s much less addictive than smoking or drinking. And while overdosing can be a deeply unpleasant, frightening experience, as the New York Times columnist Maureen Dowd found when she consumed a whole chocolate bar that would have been better cut into 16, a fatal overdose is impossible. (There has been a handful of cases in the US where people have attributed extreme violence to ingesting cannabis, but the link between cannabis-induced psychosis and violence remains unproved – and, unlike alcohol, studies suggest smoking cannabis may be associated with lower levels of domestic violence).

Where there are established risks – heavy cannabis use is associated with an increased risk of psychotic disorders – they should be set out so that, as with alcohol, people can make their own decision about whether they’re worth taking.

Banning cannabis doesn’t stop people using – the industry in the US is thought to be worth $40bn a year, much of it black market, and in the UK, 2.2 million people are estimated to have taken cannabis. But a failure to legalise and regulate it makes it less safe than it need be – users have no idea of the psychoactive strength of what they’re buying on the black market, in stark contrast to the Seattle shops, which list the THC levels of every product. Prohibition also results in millions in lost tax revenue: California, the largest state to legalise recreational cannabis, collected more than $60m in cannabis taxes in the first quarter of 2018.

Prohibition has had hugely unjust consequences. It disproportionately snares people of colour into the criminal justice system: in the UK, black people are around half as likely to report using drugs last year, but nine times more likely to be stopped and searched for drug possession and almost 12 times more likely to be convicted for cannabis possession.

The reason we have prohibition is nothing to do with preventing social harm

This should inform the way cannabis is legalised. In some places in the US, legalisation has been accompanied by expunging of historic marijuana misdemeanours, which can make it difficult to get a job or housing, from criminal records. Oakland in California has even reserved a proportion of its cannabis permits for those with a cannabis conviction in an attempt to combat the capture of the burgeoning weed industry by white, cash-rich businessmen. (Because cannabis remains federally illegal, it’s almost impossible for cannabis producers to secure bank loans.)

But the reason we have prohibition is nothing to do with preventing social harm. It’s about the queasiness politicians feel about legalising something that they perceive still has a huge social stigma attached, even though the public is now firmly in favour of legalisation.

Which brings me to the vegan burger. Take a step back and it seems bonkers that our political leaders hold firm on outlawing weed but seem loth to invoke the nanny state where it’s most needed: in avoiding catastrophic climate change. We won’t succeed in this unless we persuade people to fly less and eat less meat and dairy.

That’s a gargantuan task, made harder by the demotivating knowledge that your own efforts are only likely to matter if others match them. Yet the most politicians do is half-heartedly conjure up a few green taxes in the hope they’ll nudge people in the sort of right direction. But they’re not effective enough, and also hit the poorest most.

Time for the nanny state to get more radical. We should start by banning altogether things that have literally no function, such as bottled water in a country where it’s actually safer to drink tap water. And take a leaf out of wartime Britain – climate change is no less existential a threat – and ration activities such as flying and eating meat. If you’re not that bothered about a rare steak, you can sell your coupons to someone who can’t live without a good ribeye and feel smug as you tuck into your environmentally friendly, fake-meat alternatives.

It’s perhaps not surprising that prohibition is based on social prissiness rather than rationality. But, my goodness, we’re missing a trick. We should follow Canada, which just became the second country to legalise recreational cannabis. And go after – if not banning, then rationing – the stuff that does society real, undeniable harm.

• Sonia Sodha is an Observer columnist