All political parties over a certain size are essentially coalitions. Their members generally agree on some questions but disagree wildly on others. So long as the questions they disagree on aren’t too important, the party can hold together.
If the national agenda changes, however, the conflicts might be brought to the forefront, and as a result the party will suffer, as Labour discovered a few years ago. Labour members tended to agree on for instance education and poverty, but they simply didn’t see eye to eye on Scottish independence. So when the independence referendum was called and was felt to be higher up the agenda than education policy, the party essentially fell apart. Labour’s best chance is to make the Scottish independence question go away and make people concentrate on education and poverty again, rather than seeing these issues through an independence lens. (To some extent Corbyn has succeeded with this, convincing some left-wing Yessers to vote for Labour.)
If we call this condition Labouritis, I do wonder whether it’s fair to argue that the SNP has caught a milder dose of the disease after the Brexit referendum. Of course the SNP isn’t split down the middle, but it’s clear that there is a vocal minority of members (perhaps up to 30% of them) that are opposed to the EU and definitely don’t want to leave a post-Brexit UK in order to rejoin the EU.
As a result, I’m sensing that the SNP over the past year has gone from being a shining pro-EU beacon that made EU citizens in Scotland (like me) feel enormously better than our compatriots in the rUK, to being an uninspiring entity that tries not to offend too many people, making EU citizens in Scotland reconsider their future here. (It’s entirely clear that the SNP leadership is on our side, but they often feel rather tongue-tied, probably because some of their own members fight them every time they say something nice and coherent about the EU.)
It’s actually quite simple: If the SNP tries to keep all its members happy, they will send out conflicting signals, for instance by talking simultaneously about the importance of the EU and about wanting to join EFTA instead. The risk is that they end up appealing to nobody, so that the voters that prioritise the EU join the Greens or the Lib Dems, and the ones that are against EU membership jump ship for Corbyn’s Labour, or even for the Tories.
On the other hand, if the SNP prioritises the majority view, campaigning strongly for an independent Scotland within the EU, it might lose 30% of its members, but at least the rest will feel motivated, and the it might also attract pro-EU voters from other parties.
The alternative is to hope that the Brexit question goes away, by convincing the UK as a whole to remain within the EU. If that could be achieved, the fundamental disagreement within the SNP would again be hidden from view.
I don’t know what the best way forward is for the SNP, but I don’t think Labour’s cure for Labouritis was very effective. I hope a better remedy can be found for the SNP’s ailment. It’s possible that two pro-independence parties (one in favour of the EU and the other one against it) would do better than a broad church – but of course such a split will be disastrous in Westminster elections conducted using the FPTP electoral system.