Last week was a momentous week, the beginning of the end, perhaps, of a national depravity – the "war on drugs". The voters of Colorado and Washington passed measures to legalise marijuana, amounting to local shifts, for the moment. So we shouldn't delude ourselves that the country will be transformed overnight, but the public thinking, the public spirit is being transformed. Finally, there is a growing realisation that this "war" has produced nothing but a legacy of failure. And who wants to be associated with failure?

Let's be clear what we're discussing here. Not in question is the ravaging impact drugs can have on individuals – too many of us know people who have suffered in this way. But we need to see addiction for what it is – not a criminal matter but a public health issue, and a huge social issue, especially for the young. In fact, instead of a "war on drugs", better to call it a war on children.

In many parts of our country, a child strays a little at 14; tries a drug, can't think of any way to pay for it, and then sinks into the underground economy. Before long, he has a strike on his record, a strike that will be with him for the rest of his life. So you have a cycle of degradation, starting at 13, 14, and he never gets out of it. We now know so much about child development, the importance of the early years, how communities develop. Instead we eviscerate neighbourhoods, we strip away the infrastructure that once provided towns with resources.

And with this "war", we're talking about the erasure of a population – which was once black America, now just poor America. These are people removed from the official American story – just last week the millions of them locked up, often for non-violent drug-related crimes, did not participate in our democracy. So, at the very minimum, you are taking the poor away from the levers of power.

There is a new consensus that the economic view is becoming more influential in shifting attitudes on drugs, that the amount of money saved from policing and the amount gained through taxing legalised drugs is swaying opinion. Obviously we would all shudder to think we live in a country where only the economic collapse of a depravity like this should bring about its end. But I think it's also true that what's happening is more complicated – economic calculations meeting up with humanitarian concerns. So you have the likes of Grover Norquist, the conservative founder of Americans for Tax Reform, and Chris Christie, the Republican New Jersey governor, finding unlikely bedfellows with Russell Simmons and Danny Glover, producers on my film. All see a failed approach.

When I set off to make my film, I wanted to speak to people all over the country touched by drugs. The users and dealers and family members; but also judges and police and wardens. I expected to be a sort of court reporter, capturing an argument between these two camps.

In fact, everybody sounded like a victim. The people who work in the penal system want those jobs like they want a hole in the head; they are doing work they take no pride in. Ultimately, there are very few people who want to work in a system whose success relies on a churn of your fellow humans to lock up. And, of course – in class terms – there's far more commonality. Prison guards would tell me that they had relatives in prison, high school friends. And, hauntingly, everyone had a story about how broken the system was.

But there's a shocking fatalism in play. What I found was lots of people saying: "Eugene, I know the system is broken and I wish you well. But dream on, it is so vast and has so much bureaucratic thrust you're deluding yourself if you think it can be fixed." But these wardens would then say: "But until you do, I have to do my job, and by God, I'm an American and I'm going to do it better than the next guy."

Admirable in one sense, but it greases the wheels for the continuing operation of the machine. So a judge will quite sincerely tell you how he has no choice but to imprison a non-violent person for 20 years because of mandatory sentencing – and he's right – but then, over lunch, he'll tell you how much he regrets doing so. For a country founded in revolution, we have become spectacularly unmoored from the notion of revolutionary behaviour. Instead, we keep the bodies moving through the system.

I'm not going to pretend that the collapse of the "war on drugs" would transform life chances overnight for those born poorest in America. But, if you were to stop kneecapping many communities, you would free them to at least get their feet on the ground in normal ways. You could also save such a tremendous amount of money that you could ask yourself: what could I do that would plant a tree? What could I do in the neighbourhoods that would actually foster the values that built civilisation and would help young people find pathways other than those that end up in addiction?

Progress is not going to be made immediately on the national stage. Obama, I'm sure, would recognise the logic in the film, and then he would do what he has done for the past four years – he wakes up with the Washington machine. Four years ago, I met with his team; they said all the right things. Don't talk about a war on drugs, they said. You don't have a war against your own people. But, still, they've carried on in the same way.

What will bring about change is public demand. The public has to boo and hiss politicians who pander in this way – who say they are being tough on crime when they are destroying communities. We need to tell them that we won't let them vilify our neighbour to keep the penal system running. We will do that if we recognise that drug-mongering is no more substantial than WMD-mongering. And we know how that turned out. Americans have been an impressionable lot, but we're becoming less so. Bit by bit, we're realising that the "war on drugs" makes no sense. And, if we let politicians know this, they have no choice but to become smarter and answer our demands.