just throwing this in here, but surely employing asimovs laws of robotics would ensure we were safe maybe?
as far as AI are concerned, sure they could surpass us in time, something that notable people have indeed warned us about. When you think of about it, it really is quite scary. As for synthesis... if you equate that with AI and organics 'getting along' then you havent been paying attention to the first 2 3/4 games. The catalyst states there is no war because its just a lame way to excuse the obliteration of entire civillisations. Nothing is saved. Everything is destroyed. The younger races survive so they can also be destroyed.
You like that logic because nothing star jar states makes any logical sense. It deals in absolutes and behaves like a child when confronted with reality by shepard. If your shepard is weak willed enough to choose synthesis then star jar...cough....harbinger has accomplished his mission. Thereby removing any possible remnants of intelligence.
Some would argue, quite rightly imo, that the same can be said for destroy and control. Maybe the game was more about organics being forced into conforming to what was in effect slavery to a cycle laid down by others (leviathan) If the ending created anything it created devision of the playerbase. Maybe it was more about us 'breaking free' in which case all of the endings might well be valid..... (ignore the slide shows tho........urghhh)
" I fight for freedom. Mine, and everyone's. I fight for the right to choose our own fate. And if I die, I'll die knowing that I did everything I could to stop you. And I'll die free."
Yeah, but there are loopholes for these laws as well, no?
If something is destroyed entirely depends on the different viewpoints. I've said this before, but for us, yes, Reapers destroy organic life. For the Reapers, they store knowledge and preserve. It's simply differences in our understanding.
The logic makes sense, you just have to be willing to set aside your hatred for the Catalyst 
And for the record, just because I say the logic is sound it doesn't mean I agree with it or that I like what the Catalyst is doing. Destroy is actually my favourite ending and I picked it 3 1/2 times out of 4 (I tried Synthesis first, but immediately afterwards tried Destroy, wich I liked much more), but I'm heavily RPing when playing my Shepards, so yeah, some of my Shep's will pick Synthesis (my current one for example), some will pick Control, some Refuse, depending on their beliefs and morals.
You say that the endings might well be all valid. Yep, I agree on that. Each of us has sooo many different opinions, even if we agree in some parts, we disagree in others. I've seen people arguing for Control, against Control, for and against Destroy and Synthesis, and with that I just wanna say that everything at the end boils down to your own personal beliefs. Many people might not agree with you, others might, but still, you pick your favourite ending according to your very own beliefs and morals, so to me, there is no right or wrong. Only your 'personal right'. Everything is valid, not only your beliefs, but those of others as well.
To each their own is probably appropriate here.
The issue I have with this interpretation is that
a) it doesn't change the fact that it is inelegant writing to only show counter-examples to a purely philosophical problem within your story and
b ) it diminishes the reaper's previously set up awe inspiring vastness of perspective to them essentially being afraid of the future and
c) it ultimately renders the cycle meaningless as well
For further detailed discussion about these issues, this thread has an old discussion on them.
I absolutely understand your view points and why you feel that way, but honestly, this is only your opinion, as much as it is only my opinion that the Reapers were not reduced to 'just afraid of the future'. I didn't see it that way at all. For me it simply boils down to the Catalyst's axiom.
"Organics create synthetics to improve their own existence, but those improvements have limits. To exceed those limits, synthetics must be allowed to evolve. They must by definition surpass their creators."
It is reasonable to think that, in my opinion. They improve on themselves to surpass limits organics have, and with this alone, they already are superior to organics. And while the Catalyst is following its definition, there is no doubt that this will happen in its mind, while we think... yeah, it could happen, but it could go the other way as well.
For me the Reapers just follow this programming, not because they are afraid, but because that's what they do since a long long time, that's what their task was, they act according to that definition. I'm not even sure I'd say Leviathans were afraid of synthetics rising, but rather that they hated they lost their precious thralls and looked for a way to keep them while also successfully taming synthetics (ugh, I hate Leviathans
).
We each have our own opinion on how to see things, which is why discussions like these always go on in circles
I'm happy to accept others' view points, but so far none convinced me to hate the ending. Or the Catalyst and its logic.
Most people just want a happy ending where everyone survives and walk towards the sunset!And when they don't get that they find it inconsistent.
I know that this was an issue for some people, but not all
Actually with some in here you can have good discussions and I learned a lot in regards to why they hate the ending. I just see it differently 
Nobody says AI can't win. However, they don't and the Catalyst is the one making the absolutist statement. He doesn't speak of potential, he speaks of certainty.
I'm rather saying potential from our perspective. Yes, the Catalyst speaks of certainty, which is completely fine because of its axiom.
I'm all for Destroy as I'd rather have organics and synthetics develop on their own, conflicts or no, we don't know. We don't need an entity deciding things for us. But seeing it that way does not mean I think the Catalyst is necessarily wrong with its axiom. It's still a machine thinking like a machine.