The Scottish Greens were feeling pretty pleased with themselves this week over their policy of free bus travel for the under-22s. “Ding! Ding!”, they said in a press release, “over 100million free journeys have been made.” But Ding! Ding! what they didn’t mention was the cost. And Ding! Ding! what they also didn’t mention was that, away from shiny announcements about buses, the party is in a bad way. Let’s talk about how bad.

But first: the bus stuff. Included in the press release was a big graphic called “Free Bus Travel in Numbers” and as well as the 100million journeys, it included the fact that 700,000 young people have signed up to the scheme and 34% of them say the free travel has enabled them to “pursue new opportunities”. A number that was conspicuous by its absence though was the cost of it all, so let’s include that now: in the first year, it was £5,211,682.19 to run the scheme and £97,166,918.69 to reimburse the bus companies. Costs ongoing and rising, obviously.

I realise there’ll be plenty of folk who think this is money well spent, but what concerns me is that, whenever they’re challenged over the soaring price of bus tickets for those who still have to pay for them, Scottish ministers always point to the concessions for young people and pensioners. But what about people in poverty who don’t qualify, or people who live in rural areas, or both? Perhaps instead of giving free travel to all young people and pensioners (including those who can afford to pay) we could focus the policy on the people in need. It would also save the government some money (Ding! Ding! what a good idea!)

As it happens, I suspect the free bus policy has broad support among members and supporters of the Scottish Greens – the Left seem pretty keen on the principle of universality on the whole. But I also wonder how much internal discussion and debate there was, and could have been, about the policy before it was adopted. More specifically, I wonder how much dissent was, and is, tolerated, on this and other issues in the Scottish Greens. Having spoken to members and former members recently, I would say the answer is clear: not much.

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Let me tell you about one of the people I spoke to for example: psychotherapist Mary MacCullum Sullivan. Until recently, Ms MacCullum Sullivan was a member of the Greens, but when someone complained about some tweets she’d written on the subject of sex and gender (Ms MacCullum Sullivan is gender critical), she was reported to the conduct and complaints committee and expelled. That was it. No debate: out you go.

What Ms MacCullum Sullivan told me when I spoke to her was that she has always been careful about what she tweets and never engages in ad hominem attacks but that her recent experience was that the leadership of the Scottish Greens was unwilling to countenance different perspectives and beliefs. “I don’t believe that open debate is possible,” she said, which is pretty damning stuff coming from an intelligent, reasonable, engaged and informed party member (or former party member now she’s been kicked out).

And she’s not alone in her views. I also spoke to Helga Rhein, who’s still a member of the party but also believes discussion is not permitted within it. Ms Rhein very reasonably pointed out that a political party should allow and encourage respectful discussion on issues such as the tension between women’s rights and trans rights, but that appears to be not the case in the Greens. And I have to say it was my experience too when I tried to talk to the party about it and got a dismissive, one-line reply. Once again: that’s that, no debate.

On the face of it, the co-leaders of the Scottish Greens Patrick Harvie and Lorna Slater – who says party leaders need to be charismatic or likeable? – appear to accept that there are serious issues going on in their party. When the co-chair of their executive committee, Ellie Gomersall, resigned the other day citing “increased factionalism, hostility and toxicity”, Mr Harvie and Ms Slater issued a statement agreeing toxicity was an issue. “It needs to change,” they said.

But what were they really saying? The members and former members I’ve spoken to say there’s an atmosphere of censure and fear in the party and that’s what needed is open, respectful and robust debate. But the statement issued by Mr Harvie and Ms Slater is not a good sign in that respect.

One positive way to read their statement would be that the co-leaders have a problem with debate that’s toxic and hostile, but is their problem actually with the idea of debate itself? What they say in the statement is that there’s been an increase in factionalism, but are they actually referring to an increase in disagreement, particularly on trans issues? In other words, in apparently raising concern about toxicity, are they really just trying to tighten the clamp on their censure even further?

Whether you like the Greens or not, this issue of censure and debate is really important. Naturally, there’s always going to be a tension in a political party between private disagreement and public unity, and it’s a tension that’s most likely to be resolved if the members of the party can scent victory (hence Sir Keir Starmer’s critics keeping mostly quiet just now). Conversely, if defeat is on the cards, it’s no-holds-barred (hence the disaster zone of the Tories).

However, even if a party has an official line on a certain policy – free bus travel for under-22s or whatever it is – and members are expected to support it in public, a healthy political party must also tolerate, support and encourage debate among its members. And it certainly should not be expelling members for expressing perfectly reasonable and legal points of view, as Mary MacCullum Sullivan did.

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Do the Scottish Greens get this? I fear not. Perhaps if they were to encourage debate, and refrain from expelling people such as Ms MacCullum Sullivan, they would reduce the hostility some members and former members may be feeling about the state of their party. What many Greens are saying is that they have concerns about how the party operates but that the leadership is unwilling to listen to those concerns and may dismiss those who express them as “toxic”. But what’s really toxic is an attempt to discourage, or smother, or remove debate and disagreement.

In some ways, this is not my fight: the Scottish Greens in its current guise is so ghastly that I would rather spoil my paper than vote for them; it is not my party. But the problems besetting it are not just the problems of the Greens, they are problems that can, if we’re not careful, seep out into other groups, businesses and parties: the idea that we shouldn’t debate certain things; the idea that we should just keep quiet, nod along, and keep our concerns or opinions private. And, most worrying of all, the idea that if you do disagree, you’re toxic and must be expelled. We need to fight those ideas, now, before they take hold and damage us all.