"MY country, right or wrong” is a foolish sentiment but the American Senator Carl Schurz (an intriguing radical German-born political exile who eventually served as the 13th US Secretary for the Interior) presented a more appealing take on it in a speech almost 150 years ago.

For him, the expression was not one of passive arrogance, but rather a statement demanding principled action. “If right,” he said, a country must be “kept right” and “if wrong” it had to be “set right”. This remark has been much in my mind recently because of the increasing popularity of the dissatisfied political confessional, the “I haven’t left the party, the party has left me” apologia, the latest of which hit the press last week in the form of a lengthy explanation from the former Green MSP Andy Wightman.

I should stress that I am not criticising him. Holyrood will be the poorer without his input, particularly on land reform. Nor am I going to address here what he believes are the root causes for his departure, even though some former SNP members are keen to link their criticisms with his.

So before Twitter gets going, I am telling no one to wheest.

My beef is with the cynical view that such things prove there is no place for independence of thought and action in parties and is, in those accounts, squeezed out by imposed, heavy-handed, whipping, vicious backbiting and grimy conformity. In other words, by the mistaken view that all Scottish politics is about “my party, right or wrong”.

In fact, Schurz’s take is a much more accurate description of how people should and usually do behave. A party – and especially a democratically rooted one such as the SNP, I would contend – belongs to its members, who have not only the option but also the duty to keep it right or make it right.

Insisting on, and exercising, that democratic opportunity is a strong reason for not just joining, but also for staying and there are others which, taken together, might help us celebrate, not condemn, these institutions.

The upsurge in SNP membership after the 2014 independence referendum was, in the greatest part, a defiantly positive reaction to that defeat at a time when it was much needed. Many people wanted to assert their view that regaining statehood was unfinished business and that their choice was not one that could be swept aside.

Joining a political party is therefore often a gesture of solidarity with a cause and a desire to visibly confront those who oppose it. Such gestures, in terms of independence, remain vitally important.

Nothing would please Unionists more than a decline in the size, scale and scope of the SNP as the long-standing national party of independence with active, campaigning members in every corner of the country and a voice that is now heard and recognised at home and abroad.

But membership of the SNP has other purposes, too. It acknowledges that the achievement of independence cannot be done by individuals alone. The power of co-operation, the sharing of skills and the heft that comes from numbers are and will continue to be essential in the recovery of nationhood.

The wider Yes movement will, of course, remain a key part of that, and I value and celebrate its rich, talented and strongly committed diversity. However, there is a great advantage to have at the heart of it a substantial party of government able to deliver a referendum.

Learning to work together is another important aspect of political party membership. It is clear that in an age in which bitter division is both evidenced in, and exacerbated by, social media the ability to co-operate constructively in developing policy, negotiating difference and – most vitally of all – refusing to regard every issue as life-or-death, go-to-the wall moments of winner-take-all abusive showdown, are all valuable assets.

Being accountable for policies promised and working with those from other backgrounds to deliver them are also essential characteristics of a positive party, as are the building of political literacy and the use of polite persuasion.

Finally, successful political parties such as the SNP must – in order to survive – bring forward and put to use new talents fired with ideas and ambitions and for me seeing that happen in the SNP has been one of the most exciting experiences of the last decade.

To go from a membership of 10,000 or so when I became chief executive in 1994, to more than 100,000 some 20 years later has transformed not just the party but Scotland itself.

I do accept that some others have felt challenged by that and a few even seem to have found it threatening. For me, however, the constant renewal of the party’s core mission, the fresh commitment from those who are now convinced by it, the awakening of a new consciousness and the focusing on new means to ensure a fairer, country, has been invigorating. I am more hopeful now than ever before about the outcome of the good cause I signed on to support almost half-a-century ago.

Changing the world is, of course, the fundamental reason why people join political parties and I am with another American politician – the 34th President, Dwight D Eisenhower – when he observed that “if a political party does not have in its foundation a determination to advance a cause that is right and that is moral then it is ... merely a conspiracy to seize power.”

The foundation stone of the SNP is the cause of independence which is, for many of us, right and moral. So sticking with it – keeping going, in the words of Seamus Heaney in a profound poem about a much more difficult situation –isn’t for me a voluntary choice, subject to political or personal weather.

It is about the absolute imperative of keeping right, and, yes, sometimes setting right, the key institution working to deliver the most important change our country needs.