An honest assessment of our past may emerge from this squalid affair
Sinn Fein is so adept, so surefooted in its communications and so effective in appropriating the language of the oppressed that even its most ardent opponents are struck by the efficiency of its messaging.
Discipline is tight, very tight. Everyone is on message.
The party understands the importance of unity and consistency. Every word matters.
Its mantra is that society needs to be built upon equality and respect. This is repeated on every conceivable occasion.
And, because these are principles that all of us share, these slogans have resonance: they seem just and universal, which of course they are.
Sinn Fein is the political manifestation of the republican movement, and the narrative is that violence was necessary in order to achieve equality and respect for an oppressed people, aspirations now pursued solely by political means.
And, it follows, equality and respect is what is being demanded as a pre-condition to getting back into government.
Yet when Barry McElduff posted his infamous video, at first Sinn Fein did nothing, then it suspended him for three months, which didn't seem an especially harsh penalty for an MP who does not take his seat. Finally, nine days after the original post, McElduff resigned.
In the meantime headlines were made across the world, undermining the party and exposing it to allegations of hypocrisy and cynicism.
One of the biggest mistakes that Sinn Fein made in handling the crisis was its false assumption that it could be turned into a "one day wonder" - that media coverage would be confined into a single day and normal service would swiftly resume.
This was not the case. The media, both print and broadcast has pursued this relentlessly. The press pack in full flow is a truly formidable force not to be underestimated.
There may be several reasons for the reaction in the media: the sheer inanity of the video itself, the fact the story broke at a quiet time, the international coverage which encouraged further probing, and the extraordinary public reaction.
And then there was the poignancy of the Miriam O'Callaghan interview with Alan Black and the fact that it was broadcast on RTE - this was the coup de grace.
A resurgent Sinn Fein leadership in the south, with its aspirations for government, could not suffer McElduff surviving as an MP after that. If any in the party thought the video funny when they first saw it, that moving interview will have wiped the smile off their faces.
How did this happen and why?
Only Barry McElduff knows what he meant by appearing in a supposedly comical video searching for bread in a shop with a Kingsmill loaf on his head.
It may, as he claims, have been a joke, and he might not have known about the significance of the day on which he posted it. But it was on the anniversary of the Kingsmills massacre and if he didn't know, he should have done.
If he wasn't gloating over a vile atrocity, he was proving himself to be an idiot. An off-message idiot.
What made the situation even worse was that this was no ordinary IRA attack. It was a blatantly sectarian massacre, carried out under the nom de guerre the Republican Action Force: the IRA did not claim it and has not done so to this day.
The attack was seen at the time as a republican response to the loyalist killings of six Catholics in the Reavey and O'Dowd families the day before.
Presumably there were those in the IRA's support base who welcomed it back then. 'Take one of ours and we'll take more of yours.'
It reminds us of just how squalid and sickening the conflict was at its height. There was no respect shown to victims and the only equality in sectarian slaughter is that of the grief suffered by survivors and the bereaved.
McElduff's resignation will prompt a by-election. Sinn Fein will win it. Anyone who thinks otherwise does not understand politics in this part of the world.
Yet the incident has dented the Sinn Fein narrative, especially the bit that asserts that republicans "don't have a sectarian bone" in their bodies. Perhaps this is a good thing. If a more open and honest assessment of the past, one in which all sides committed unspeakable acts, were to emerge from this, we might be able to progress to a shared idea of what "equality and respect" means.
And at least this depressing episode has led to two encouraging developments. The first was Sinn Fein's John O'Dowd, who lost family members the day before Kingsmill, describing the murders as shameful and purely sectarian.
The second was the searingly moving interview given by Kingsmill survivor Alan Black.
Mr Black's unwavering account to RTE of what happened on that day, of him lying on the roadside alongside his dead workmates and of his apprentice calling for his mother before being shot in the face, serves to remind us of the darkest of days.
He also described a member of the Reavey family calling at his home with Christmas presents.
Two families united in grief. There was dignity in that gesture, and respect.
Nick Garbutt runs Nick Garbutt PR