You assume that all previous synthetics were exactly like the Geth or that every previous organic/synthetic conflict came about in the same exact way.
Read my post again. If there is someone on this thread jumping into conclusions it's you.
All we have are vague information that the "Leviathens" attempted to end Organic and Synthetic wars by what creating another synthetic? what the hell?
Did the Leviathens attempted to intervene? did the Leviathens attempted to reason with the Synthetics? did the Leviathens attempted to aid the organics in-terms of diplomacy and military power? No? so what did they do? they just sat there in space and observe Organics being wiped out by rogue AI'S or because there was misunderstandings?
throughout the trilogy there are alot and I mean alot of evidences of past Organics being wiped out by the Reapers. We don't know if those Organics in their respective cycles had synthetics with them... what we do know is that the Reapers enjoys the genocide of the organics or anything which are allied with the Organics including synthetics. We have that planet with a "great rift" it could have come from a Synthetic rail gun who are allied with the Organics themselves or it could have come from the Organics themselves it is vague.
The prothean cycle did not mention any synthetics being created in that cycle so the Reapers thought "yoh these cycle is reaching it's peak time to destroy them."
The last known Organic - Synthetic war was from the cycle of the Leviathens themselves. The recent Organic - Synthetic war is the MORNING WAR this war is the key in invalidating all claims of your precious Casper. The Geth is proof that PEACE can be achieve through diplomacy not irrational actions, However the Quarians acted in haste which prompted them [Geth] to allie with the other Synthetics... the REAPERS! and what's disturbing is; instead of classifying the Geth as also a "part of the organic - synthetic war problem" it didn't... it helped them even contacted them and told them that the Reapers can provide aid while an Organic race which attempted to make peace with the Reapers got totally wiped out in a heartbeat according to Javik. Why is that so? are the Reapers biased? what is their true motive? to end all wars? or to maintain hegemony and be worshiped as gods? LEGION AND HIS PEOPLE REJECTS THAT IDEOLOGY they are willing to help all Organics to defeat the reapers this then invalidates all reasons of Casper that "the created will always rebel against the creator" no... the real reason for organic and synthetic war is "the created has malfunctioned or does not understand its true purpose" that purpose can mean anything. The Geth's purpose was existence not through the use of force. If the Leviathen are so wise they should have thought about this during the past cycles, if the Synthetics in that cycle can not be reasoned with then they should have aided the Organics but instead they created a Synthetic which obviously sided with the synthetic race to defeat the organics themselves and that is the true purpose of the catalyst but it has re-named it as "preemptive war to prevent organic synthetic war" the catalyst only harvested organics nothing more... where are the other synthetics that rebeled against their creators during the cycle of the leviathens? what happened to them? if they hated the organics so much , their masters... we should have encountered them as allies of the reapers in ME1, ME2, AND ME3, but there was none. NONE... which leads me to suspect that those synthetics realized that the Reapers is a bigger threat and allied with their creators in the last moments of the war but was too little too late.
Now here's another question about the motive of the catalyst, what if the Quarians accepted defeat from the Geth and choose not to re-take rannoch but re-locate to another system? so there is already peace... then the Reapers attacked... do you think the Catalyst will also attack the Neutral Geths? I don't think so.