I did read your post before you edited it. Why did you remove it?
I was tired when I wrote it and it seemed overly aggressive in tone when I reread it. I was planning to make much the same points without some of the polemical jabs, but I got distracted went and made dinner instead.
I didn't actually mention it in the removed post, but it's worth saying that I don't locate the source of the SWP/PBPA's recent behaviour in some kind of sectarian original sin. It flows from the PBPA gamble. I actually think that the SWP were sincere enough about the ULA in its early days. Even when they set up "Enough!", which trespassed rather too much on the ULA's supposed role, they were still putting resources into the ULA.
It's the effective relaunch of PBPA and the massive shift of resources into it which indicated the change in direction. And that rather amusing leaked circular slagging off everyone else gave an accidental insight into the reasons - the SWP leadership was getting extremely frustrated at the inevitable overheads of working with others on an equal basis, particularly the tiresome task of actually winning support for their views and proposals. The frustration also stemmed from the failure of the ULA to grow on the ground. Without the fetters allegedly imposed by the "conservatism" of Collins or the WUAG and the irritating encumbrance of the Socialist Party, the SWP would use PBPA to demonstrate the superiority of their dynamic leadership and show the huge gains that a more, ahem, vibrant left could make. This is of course in the context of a perspective which has held for more than ten (twelve? fifteen?) years that big advances for the left are there to be made.*
Everything else flows from doubling down on that over and over. It has led internally to a greater and greater emphasis on PBPA work (and inevitably PBPA politics). And from an external point of view it led to what seems like destructive behaviour because building the PBPA came first. Lots of people on the left have an extremely jaundiced view of the SWP and see it as almost unchanging. I actually think the most interesting thing about PBPA is exactly how much it has changed the SWP.
As I said in the removed post, there are two different strands to the SWP/PBPA's "belligerence" when it comes to standing candidates in other group's target seats. 1) moves which are about replacing Collins with Brid Smith. This ultimately included the European election stunt, where hindering the Socialist Party was just a bonus. 2) gratuitously standing no hopers against incumbents or serious contenders. The first is a core interest that they have invested a great deal in. The second, I think, is mostly an artefact of a hope/expectation that the local elections would leave them in a dominant electoral position on the left, with PBPA established as the only or at least the main game in town. As that hasn't worked out, I don't think the SWP/PBPA gains much from antagonising everyone else.
As such, there may well be scope for agreements of the sort which centre around the SWP/PBPA knocking it off with the no hoper vandalism. I don't see how there can be any substantive "unity" involving both Collins and the SWP however. The Socialist Party, it should be noted, has nothing invested in standing candidates in other people's targets and I believe the last time it did anything even slightly comparable was more than 20 years ago.
You may, of course, have a different perspective on all of this, which I would of course be interested to hear.
*eventually this perspective will be right on the stopped clock principle.