I don't think getting the soul is the best comparison, because I don't think Buffy would have wanted to stop Spike if she knew what he was up to. Better examples are helping Dawn resurrect Joyce, offering Buffy money from his demon egg scheme and dumping Katrina's body in the river.
I like to imagine that a new timeline was created in IWRY, just like it did with the Wishverse, so that a Buffy and a still human Angel remained behind when time was turned back.
Elaboration: In Doppelgangland, Anya and Willow are able to pull a second Willow from a timeline that shouldn't exists anymore. If that timeline can exists, then maybe there still exists a timeline where Angel remained human after going to the Oracles and time never turned back. I can't explain it better. I am not good with time paradoxes.
Oh, I see what you mean. I think that the problem is that the discussion unraveled into a different direction. A member mentioned that they liked Spuffy because they didn’t like Angel’s attitude in this episode. The response to that comment was about the qualities of Spike as a potential partner, which was answered as of why Spike wasn’t the monster described and which comparison should be considered fair by the first member. Leading to the ensuing discussion of whether Buffy asked Spike to get a soul. Not time paradox at all, just plain same old discussion.
But yes, we don’t know exactly what would have happened. Maybe Buffy and Angel would have worked it out, so Ensouled!Spike would have never happened, or maybe it would have been the last straw for Buffy’s relationship with Angel, still leading somehow to an scenario where Spike gets his soul. I’d personally prefer the second scenario, but the first scenario would be more likely to have happened. But it totally depends on the reaction of Buffy to Angel's decision and his final choice, I agree that remembering is Buffy's prerogative but being human or a vampire is Angel's decision.