@MrFob:
I'll try to recreate the structure of the debate I feel we lost in the exchange. In this post, I'll distinguish between the complete evolutionary stasis we were discussing, and the limited technological stasis of the Reapers' extinction cycle, and of any other means one might use to prevent the organic/synthetic extinction scenario the Catalyst claims is inevitable, if that claim is true and if no permanent solution can be found.
(1) Complete evolutionary stasis
We had been discussing the question of whether static life can exist, and whether it is meaningful for life to exist if it's static in some way, because the extinction cycle prevented any change in the circumstances of organic, and because I presented the possibility for a temporary stasis in order to avoid disaster.
I think the basic question "Can static life exist", preliminarily defined as life that isn't subject to the forces of evolution, while interesting, is somewhat academic. I can't prove that it can exist because I'd have to demonstrate such life in concept and prove that the concept is viable, and you can't prove that it can't exist because all that's needed for my claim to be true is that it is conceivable and can possibly exist, not that it actually exists, even if I can't demonstrate its viability. Even more importantly, all definitions of life we can refer to in order to lay the groundworks for our claims don't take synthetic life into account, and since synthetic life exists in the MEU, those definitions fall short. Which means that with the means at our disposal, we won't be able to come to a conclusion.
I am prepared to concede your point, however, if we extend the meaning of "evolution" beyond the strictly biological and accept the "mental evolution" you mentioned in your last answer as being part of an ecosystem's natural evolution once it has achieved intelligence, and in addition, set the condition that environments don't remain static for an ecosystem's remaining lifetime after it has achieved intelligence. I think that's a reasonable condition to set, even if it's not necessarily true for all imaginable systems.
I'm usually not fond of changing the meaning of "evolution" in debates about these things, since it plays into common misconceptions of evolution - advancement does not equal evolution - but I think it may clear up some confusion here. I think a civilization *can* stop the mechanisms of biological evolution for an ecosystem and continue to exist, but a civilization with that ability will continue to change in response to changing circumstances. It will just be a directed process, just as in the case of synthetic life in your example.
With that said, I propose we lay that debate to rest. It is actually not relevant to ME3's plot, because none of the participants of the conflict make such claims, not even implicitly. The Reapers don't aim for a total stasis, they aim for a technological stasis in one area only, namely the development of synthetic life.
(2) Limited technological stasis
I think, in this are there is something I may not have taken into account previously: the fact that we create our own evolutionary environment to some extent (I'm using the term in the extended meaning proposed above), and that limitations drive advancement. I think a case can be made that it is impossible for a technological civilization to arise in an ecosystem that just accepts its limitations and remains static. It is debatable - see above - if such a system can exist at all, but even if it exists, it will never be able to extend its reach. This means, that if a civilization reaches the point where the Reapers target it for extinction, it is necessarily one that chafes at its limitations. Again, it is conceivable that this changes at some point after the system achieved sentience and technology, but this would be tantamount to changing its fundamental nature. In order to illustrate this, consider that for human civilization to get there, we'd have to eliminate competition - in the most general sense, not just economic, and on every level, not just between individuals. I think a case can be made that whatever the result, it wouldn't be a human civilization any more, in the sense that we wouldn't recognize its people as ourselves. The species may not care about changing its nature, but then, if it achieves stasis, then the Reapers wouldn't target it for extinction, and it would be a dead end of evolution as well.
Ironically, this feeds into the Reapers' rationale for the extinction cycle, for it means you won't be able to prevent advancement except through a kind of totalitarian control that would make North Korea look soft - or through extinction, and the latter is quite a bit more economical. On the other hand, it may be the reason for recognizing that the cycle won't work anymore: they almost came too late this time. Eventually, they *will* come too late, and they don't have the resources to keep the whole galaxy subjugated and subject to totalitarian control.
(3) Conclusions for the Catalyst's reasoning
This means that if the Catalyst's reasoning stayed intact after the Crucible docked, then it should never have accepted its own destruction or subsumption (Destroy or Control). That would go against its fundamental purpose, for it means it will forego any agency over the future, without even the remotest assertion that the problem it was built to solve will be addressed at all. On the other hand, if the Crucible dominated its thinking to a degree that made it accept those options against its own interests, it should've been powerful enough to just make it stop as well, because stopping and remaining alive to possibly reclaim agency in the future is better than being destroyed or subsumed with your purpose unfulfilled.
I can only think of one scenario that fits this logic without contradiction or turning the Catalyst incoherent: The designers of the Crucible designed the scenarios, and "just stop and wait" wasn't on their agenda. That actually makes sense.
Only the writers clearly didn't want this interpretation. They wanted this "god-analogue that offers the ultimate boon". They didn't want galactic civilization or its representative, Shepard, to have primary agency over the future, only secondary agency by choosing from the set of ultimate boons offered by the god analogue. And that, I believe, is the main element that made the endings so unpleasant in the end.
In the last few days, I've been writing up an alternative exposition for the same choices we have that may have mitigated that effect drastically. I'll post it in a separate thread once it's ready.