Paging QMR...
Now if you'll excuse me, I'll just sit back with this bucket of popcorn.
you didn't actually page me, tho :'(. Nonetheless, I shall provide the shitpost to end all shitposts to make sure this new fan ends up playing for glorious Team Quarian,
or at least has a more informed, less biased view of the full narrative.
First off OP, your post has some incorrect and rather lofty assumptions.
1) Legion did not make any of that clear to anyone, let alone the quarians. It doesn't go to a legitimate authority like the Admiralty Board (you can take it on Tali's mission, but it just sits there trolling and doesn't make any attempt to establish diplomatic connections or share pertinent information with them), nor the Council (although they probably would have found a way to be useless still, considering they think it's a simple mech if you take it to the meeting with them) nor even an official representative of the Alliance government.The only people it interacts with in its "Liason" role are Shep & Co. (i.e. a bunch of Cerberus affiliated terrorists, among them possibly one random quarian). For all the quarians and the rest of the galaxy at large know, the geth are those things that revolved when the quarians benignly tried to turn them off because they weren't working properly, then genocided and ethnically cleansed their species until 99.5% of them (1 million of 2 billion survived the genocide according to
Ascension) were slaughtered and the survivors forced to flee their Homeworld and colonies.
Legion is also hardly a reliable source. It objectively lies and engages in misinformation on multiple occasions (unprovokedly stealing Tali's omnitool data, claiming it is not allied with the Reapers/does not posses their code upgrades, transferring the geth programs from the Fighter Squadrons server into Prime platforms that then ambush the group, rather than deleting them). Your assertion of it bearing no "ill will" also does not mesh with it threatening the quarians with revenge and violence on at least one occasion. You should no more trust it's word on the geth-quarian conflict as impartial than you should Tali's, or than you would Wrex's on the Genophage. It has a vested interest in persuading you to its side like everyone else.
https://www.youtube....61p8KJI#t=3m15s
^"no Ill will"
2) The quarians "did not start a needless war when the Reapers are wiping out the galaxy", the war started before that. By your first visit to the Citadel hours after Earth is attacked, there is a Specter Terminal entry waiting for you that states the quarians have already mobilized for conflict and headed for the veil. The war then goes on for 17 days (according to Admiral Han'Gerrel) with the quarians easily demolishing the geth and driving them from all 4 quarian pre-war systems until only the geth on and over Rannoch remain.
Then the Reapers show up in the Perseus Veil, get involved on the side of the geth and halt the quarians via neturalizing their jamming weapon. I suppose someone else could have informed the quarians that the Reapers had arrived in the middle of their campaign, but no one did until the Reapers had already used the upgraded geth to trap the Migrant Fleet over Rannoch. The quarians are galactic pariahs that most of the other species hate, and hardly communicate with except to tell them to stay out of their space, so it makes sense there was no pertinent communication in time.
-Some other points
The war was in no way "needless". First off, there are the practical considerations to the quarians' utility to the war effort. As the Fleet sits, it's cargo holds are full of what are in essence shantytowns packed with quarian civilians. If it tried to go to war without somewhere relatively safe to offload them and the agricultural/manufacturing equipment to sustain them, not only would the quarian species be risking extinction at the hands of the Reapers (who are a far greater threat than the geth) if they lost even 1 Liveship (all 3 of which are required to sustain the population), you wouldn't be able to use the ships for anything except shooting at the Reapers anyway. The primary reason Hackett sends you to get the quarians is logistical (i.e. the massive number of ships means you can ferry lots of troops and supplies with them, an example being the horde of krogan troops, who have no ships to reach the battlefronts), which you can't do with millions of quarian noncombatants already taking up that space. Without offloading the civvies, the quarians can't really make themselves all that useful to the war effort. Han'Gerrel states as much in ME2.
Tali: "We might need the Fleet to fight the Reapers, Admiral"
Gerrel: "Then we need a world to shelter our noncombatants while we do it."
However, it can't just be any world. The Council in the past has displayed outright hostility toward the quarians when they have tried to establish colonies on even barely habitable worlds.
http://masseffect.wikia.com/wiki/Ekuna
so they aren't going to lend a hand. Meanwhile as mentioned before, the geth have made no attempts to negotiate or even communicate with the quarians for 3 centuries. Nevermind that, the peace envoys that were sent by the Council were blown out of the sky according to
Revelation so what would be the point in the quarians trying to do the same? For all they know, they'd just be needlessly sending people to their death and broadcasting their intentions of regaining their planets, giving the geth time to prepare for their offensive, leading to more deaths and a longer campaign before they can start helping against the Reapers. Considering that the quarians have developed a way to easily defeat the geth with almost no casualties (that the Reapers would help the geth is not known at the time of the invasion), they'd be stupid to not sieze the opportunity they've been given.
Outside of the scope of the war, the quarians need somewhere to settle soon, because their mode of living is unsustainable. Many of their old ships are falling apart and becoming irreperable, and they are even beginning to have trouble breeding due to low birthrates (they can't sustain more than 17 million people living on the ships) leading to genetic problems (this is part of the reason for the Pilgrimage, to slow the onset of health problems due to inbreeding by making sure individuals mate outside their birth ship). An estimate in the novel
Ascension gives them 90 years to extinction as is. They have been looking for suitable colony worlds for quite some time, sending out ships like the
Cyniad to scout for habitable planets, but their low tolerance biology makes finding a suitable world far more difficult, and even if they do they have the hostile Council (who claims vast amounts of the galaxy) to contend with, limiting the number of candidates even further. They evolved to work on Rannoch, and the difference in re-adapting to its environment vs even a tolerable colony world is described as "the difference between 60 and 600 years". By contrast, the geth have no need for the planet at all. They live in space and draw resources from asteroids. Legion says that they only maintain control of these planets out of some sort of sense of respect toward the memory of the quarians they killed, along with an expectation that they'll return but it only elucidates this to Shepard. If if we assume its word to be true, why does it do this? Shepard isn't a quarian so why should s/he care? For all the quarians know, the geth are just squatting on the Homeworld they forcibly annexed out of further spite to them and practically goading them to try and take it back, or worse (given that the only geth reperesentatives outside the Veil in 3 centuries have been Reaper allies) plotting something far more insidious. Daro'Xen's weapon gives them the first means in over 10 generations to eliminate this potential threat, the means to give their children a future and a half decent standard of living. They'd have to be daft not to take it.
Finally there are other, more subjective reasons, like why should the quarians simply sit around wetting their suits, or going and begging the geth to throw them a bone? That planet is theirs. They were there first, and the geth forcibly annexed it. They have more than every right to do the same right back if they have the means, especially considering that the geth could give up the planet at literally no loss and go live on some asteroids in a remote part of the galaxy as mentioned. That they don't do this (i.e. exactly the same thing the quarians did when facing defeat in the Morning War) when they realize the quarians have their number, and would rather ally with the Reapers and try to destroy every organic in the galaxy than give up Rannoch, is just nonsensical. In fact, why did the geth not make any preparations for the Reaper war in the first place? The quarians spend the 6 months between ME2 and 3 arming every single one of their ships for combat. The geth spend it building a functionally useless (for combat) Dyson Sphere to hide in.
While we're at it, why do we assume the geth are even worthy of any moral consideration at all? The brightest AI scientists of the ME universe, Council Law, and the general public, all seem convinced that they're just highly advanced machines, not lifeforms at all. Only an Alliance Soldier who doesn't even have a college education (Shep) can (but isn't required to) express otherwise. Frankly, I don't see the evidence for them being anything more than malfunctioning toasters in desperate need of a commercial recall. "Genocide" is a laughable term for trying to unplug your computer after it freezes up and the power button ceases to work. If you take this line of reasoning (as pretty much everyone else in universe seems to), the conflict is even more simple. There are a few people in universe who criticize the quarian timing of the invasion close to the Reaper one (mostly those ignorant of the knowledge the player is given), but virtually everyone is relieved if they finally destroy the geth threat.
Try playing through the games again while taking the less traveled Renegade (i.e. supporting the quarians instead of the geth) path in relation to the conflict (Eliminate the Heretics or Sell Legion to Cerberus, pick dialouge that supports the war etc.). The quarians get a much fairer treatment in this regard. Also read
Revelation and
Ascenscion as they both provide exposition on the conflict that the games (particularly ME3, which is blatantly one sided) sorely lack. I hear these sorts of critcisms all the time (along with similar ones of the Salarians/Turians in relation to the Genophage) and it is usually by people who are new to the series and haven't actually gotten to hear all the arguments in question that multiple playthroughs and a more in depth following of the lore provide.