So, you want to have a serious conversation about drugs?

Prepare to speak out against the two major parties who are united in their opposition and don’t expect a fair hearing from the capital city tabloids. Talkback radio won’t be kind either.

Society is told to look at illegal drugs equally, with fear and derision. Drugs are the domain of delinquents and good-for-nothing young people and no serious conversation is required, unless you’re talking about crackdowns, raids and policing.

But the tide has changed on medicinal cannabis in Australia, so maybe public opinion is shifting on recreational use too?

The Greens certainly hope so, announcing their a plan to legalise recreational cannabis while citing 55 per cent public support. Sales would be limited to people over 18, there would be no advertising, the drug would be sold in plain packaging and the tax revenue would fund education and drug treatment programs.

“Prohibition has failed,” the Greens leader said. Di Natale, who was a doctor before he was a senator, continued: “the ‘tough on drugs’ approach causes enormous harm. It drives people away from getting help when they need it and exposes them to a dangerous black market.”

The Greens’ policy would turn that black market into a lucrative one for the budget bottom line. Independent Parliamentary Budget Office costings released by the Greens show the policy would create a $1.8 billion a year windfall for the budget.

A 25 per cent excise on sales, like the one applied to tobacco, along with GST and a reduction in law enforcement costs, would generate $3.5 billion for the government by 2020-21.

Of course, the major parties have been quick to denounce the proposal. The federal health minister, Greg Hunt, said the policy was not “safe, responsible or something which should be allowed.”

The opposition leader, Bill Shorten, called the announcement “political clickbait” and said the Greens want to legalise ecstasy. Cripes! (It’s not true, although the Greens platform includes decriminalising all drugs.)

Shorten was right about one thing. The announcement is political clickbait.

Remember back a few weeks to the Greens’ loss in Batman. Labor’s popular trade unionist, Ged Kearney, is now installed in Canberra after the Greens failed to break through Melbourne’s Bell Street curtain.

Column inch after column inch has already been dedicated to this result, but most conceded the Greens’ flagship anti-Adani coal mine campaign failed to cut through. Although heinous, the reality of a mine which will be a bigger greenhouse gas emitter than the entire country of New Zealand wasn’t close enough to home.

The Greens, then, are clearly looking for something will resonate in their would-be heartland: the inner city. Is legalising cannabis the policy to do it?

Head to the official-sounding http://drugs.org.au/ and you will be under no false pretences about who the Greens are targeting with their campaign website. The site, titled “Just Legalise It”, is loaded with pictures of bright-looking young people enjoying a picnic and going to a gig. The kind of people who might turn their vote Green, if they haven’t already.

But the Greens are not seen as a governing force. Perhaps the lesson of Batman is that voters will choose a party with a real chance of governing in the hope that at least some progressive positions will be adopted. The Greens just don’t have that kind of clout.

Fans of legalising cannabis will take the win if, at some point in the future, Labor comes around to the idea and makes it happen. The Greens will cry foul over policy plagiarism, because a win on principle in this scenario doesn’t translate to political capital for the minor party.

And “makes it happen” is the key phrase here. Cannabis is a state issue. But it could pay off the Greens, who probably now realise they need to pursue issues closer to home, and to capture the kind of attention that only comes with announcing policies others are quick to label controversial.

What makes cannabis so controversial? Everyone who says we have to see it that way.

“We need to get real about cannabis. Almost seven million Australians have tried or used cannabis socially but right now just having a small amount of cannabis in your possession could get you a criminal record,” Di Natale said.

In 2008, Malcolm Turnbull, then opposition leader, gleefully told Tony Jones on ABC’s Q&A: “Yes, yes, yes. Yes, I’ve smoked pot. There you go.” This was a very different era, of course, where Turnbull was prepared to say Tony Abbott’s climate change policy was “bullshit”. How things have changed.

Some things don’t change, though. Or take ages doing it.

Would politics be better if policy could adapt faster? Chances are a politician will say the slow and deliberative process is what ensures we don’t rush a slew of madcap, harebrained policies through parliament and then need to apply constant legislative patches.

But that’s exactly what we have now: this slow process hasn’t stopped bad policy before. Once an idea finds its political legs, it’s hard to stop it running.

Before alcohol prohibition was adopted in the United States, Sweden and Russia in the early decades of the 20th century, expert commissions and committees in all three of those countries warned against the policy. It was later repealed after disastrous results.

But few experts are able to put a stop to an idea with political backing and popular support. The experts now calling for an end to drug prohibition probably feel they have something in common with those ignored a century ago.

Australia’s serious conversation about drugs has a long way to go. In Melbourne last month, 3AW host Tom Elliott said a safe-injecting room in North Richmond was a “Trojan horse”, predicted “probably” all drugs would be legal in five years in Victoria and said: “This is the thin edge of the wedge stuff.”

If all progressive proposals about drugs have to be thin edges of wedges, then maybe the Greens’ announcement could be a thin edge of the wedge to force the serious conversation about drugs that Australia needs to have.

Jasper Lindell is Woroni’s political columnist and a former news editor