Whichever side of the argument you stand on, this is one of the most divisive things I've ever seen happen in HE. And I've seen a lot.
One thing I'd never do under any pretext is to undermine others' action by marking their work for them. But, just as much, I would never do what I've seen fellow union members do in terms of shaming those colleagues on social media, dropping broad hints as to their conduct but without actually naming them directly. Nor I would I ever call those who did capitulate to the pressure to mark others' work - at my instutition this was considerable; I know as I was on the receiving end of it - 'scabs'. People have their own pressures to contend with and they have made this decision - a difficult one by any reckoning - according to their concsciences just as I've had the liberty to do the same.
This undermining of the MAB has been done to me. I'm not remotely happy about it, and am not inclined to pretend I am. If the colleague concerned asked me about it, I'd answer frankly to this effect. But lack of future trust aside, I would not treat that colleague with anything other than the utmost professionalism, because I'm an adult.
I'm sorry to the HoDs who have suffered so much as a result of this never-ending dispute. If we are angry with anyone, it should not be colleagues who have suffered alongside us, or Branch, who have tried to support us. The people who should earn our disdain are for me, my university's horribly draconian senior management - we really are up their with the worst of the sector in terms of their contemptuous treatment of staff - UCEA, and in no small part Jo Grady for her inept handling of the whole situation.
I can't see a resolution at the next round of talks. The last three months alone have cost me into the thousands; we are well into sunk costs fallacy here. It seems everyone is suffering but senior management.
I don't know how I'd vote in another ballot, or know what, now we're so deep into the mire, is the best way out of it. What a badly handled mess this is.