While I can agree the handling could have been better, I disagree that it's the mess you make it out to be.
(SPOILER)The only characters really acting irrational is Yukari and to a lesser extent, Aigis herself but since these two were the closest to the Protagonist in-game story, it makes sense they would have the most grief. The rest of the cast is pretty much uncertain about what to do except for Akihiko and Ken who happen to be better off since they are the ones who have had to deal with grief the most out of the whole cast, even in the Journey, these are the two who ultimately bounced back from the most devastating revelations and twists of the story first. Even Mitsuru's decision to stand by Yukari makes sense when you put into context how stubborn she usually is and how important promises are to her, even then, I would argue that she would have probably talked Yukari out of it had she won the conflict, but we'll never know since Aigis won.
We're also dealing with a group who until a few days before the story started, had lost their memories concerning the Dark Hour and had them returned, and now just lost the one person who held them together throughout all the hardships of the previous year; the anchor of the team that brought everyone together and now they have to learn to cope without. So emotions are raw and high, and in this grief stricken state, it makes sense the party wouldn't exactly be rational. Hell in the original game, the party would mope for weeks after Shinji's death, the betrayal, and the revelations of Ryoji, in all those cases the party knew they had time and often were making choices that reflected what they personally wanted to do such as continue the fight or finally call it quits. Here, as you said, the world is coming apart from temporal distortions, so time is not on their side and their actions wasn't about their personal stake but one that would affect the rest of the world. They had to make a decision soon in this state of grief, and they chose, for better of for worse. The only real conflict came from the two extremes of Akihiko and Yukari and Aigis simply chose to stop both of them before they did create irreparable damage to their groups friendship. Junpei's only conflict was that he seriously wanted to wait and think things through but the party didn't exactly have time to search their feelings, especially if Yukari or Akihiko started to aggressively attack the other groups for their items. Even when all was said, Aigis chose a fourth option which was to learn the truth of what really happened as opposed to change the future or let things be without knowing. Grief is hard to write, because we all want to think we could be rational, but here it was not.
Of anything, I feel the missed opportunity here was that the choice they made should have been left up to the player to see where they would have sided. Regardless, The Answer is still important to the series because P4 Arena confirms it is canon, whether you liked it or not, but I still feel it was an interesting place to take the series even if it was obvious the devs made it quickly and without the care the main game had.
Anyway, if we want to keep debating this, I'm fine with that but let's move this to another thread so as not to derail this thread, especially since we should really be talking about the awesomeness of Persona 2 right now. We can pick this up in another thread or later when FL crosses that bridge.