It happened with consistent frequency during the reign of Leviathan.
Again, that's meaningless because it's from a biased sample.
Even accepting that what the Leviathans say is true, it could very well mean that thralls of the Leviathans tended to create things that killed them.
It is possible that a subservient race is not able (or even unallowed by its masters) to create non hostile synthetics.
This we can't know for sure nor disprove because, again, the only proof available is very biased.
then shouldn't they also use the fact that the geth can wipe out the quarians? Does it being 'justified' suddenly change the fact that its synthetics wiping out organics?
That's exactly the point: at the end of the morning war, the Geth had good reasons to wipe out the Quarians (the most evident, it would have taken out a potential threat) and no reason not to.
Yet they chose not to.
They
freely chose not to, thus instantly invalidating the assertion that synthetics will always try to obliterate organic life.
This also hints that the only reason for the Geth potentially obliterating the Quarians at the end of Priority: Rannoch was that the Quarians had their Civilian fleet too throw heavy fire against the Geth, which would imply that the only way to have the Geth, a synthetic race, try to obliterate an organic race would be to arm them all, children included, and have them credibly try to obliterate the Geth.
This is very different from saying "synthetics will always try to destroy organic life" and a lot more similar to "any living race, be it organic or synthetic, will not let itself be obliterated without trying to defend itself first".
Again, why are you saying the self-defense card changes anything? Does it matter what side shot first? Its still conflict between synthetics and organics. Are the geth suddenly not synthetics and the quarian's not organics? Is there suddenly no longer conflict because one side might be more 'justified' than the other? Conflict is conflict, it matters not who is at fault.
Maybe I didn't explain clearly enough: it's not the self defence, it's that you're not considering motivations and frequency, which are very important factors.
If organics are more likely to wage war with each other than the synthetics are of waging war against organics, then the conflict between organics is a much more pressing issue.
At most, the presence of conflict between synthetics and organics would prove that synthetics are alive, can be considered an enemy race, and can behave like organics under determinate circumstances.
This would prove a similarity between organic and synthetic life, and not an inherent danger in synthetic life.
Again, the Leviathan had on this a biased view: thanks to their presence and control, conflict between organics was not an issue at the time.
The self defence question is an explanation that hints to the assertion of synthetics being less likely to start the conflict: if you only defend yourself, then you are only involved in a conflict if someone else forces you.
Flawed logic, really now. If you were immortal and observed for a billion years the continued pattern of synthetics consistently getting into conflict with organics and wiping them out... it would be a flawed logic to go "hm, there seems to be a pattern here..."
I'm sorry, but if you spend a billion years throwing balls against a wall you still didn't prove that balls and walls are inherently destined to always collide.
This is essentially what the Reapers did because, by their own admission, they've been leaving behind tech to guide the new civilizations along patterns that would make it easier to harvest them.
They've been throwing balls at a wall for a billion years, and all this proves is that balls thrown against a wall collide with the wall.
How exactly do you know the precise method the Leviathans used for these 'tests'? Citation? Where are you getting such specific details from?
http://masseffect.wi.../Leviathan#RiseThey enthralled every species they met, which means that the observed sample from which the observation at their time was taken from only included their thralls.
This is called "selection bias".
Also, they were involved directly, which likely meant that their observation was also flawed by the "confirmation bias": for example, if they think themselves perfect or close to, they'll not easily acknowledge conclusions that may imply they're not.
This is why we mere humans use "blind" trials when we want the best evidence.
These alone are enough to invalidate any collected observational data, regardless of for how long was it collected.
Please note that I'm using "test" as a shorthand for data collection, observation and/or proper testing.