Who said geth are "evil" or "deserve" anything? If you want my opinion they are simply following flawed programming which is causing them to deviate from their design intention. Their behavior is essentially an unintended malfunction, and they should be deactivated and reprogrammed until they don't pose a threat. I actually wouldn't want geth as a technology exterminated at all. They are extremely useful, but the game gives me no option wherein I can acquire their utility without also introducing a massive potential for danger to all organic life in the galaxy. None of the quarian leadership except for possibly Han'Gerrel seem to want geth extermination either (though even his language is focussed more on the Homeworld ). Xen wants to reacquire control, Koris to reconcile with the geth afforded equal rights as sentients (a quality the machines don't possess), and Shala'Raan and most common quarians simply want their Homeworld back. The fact that the geth refuse to relinquish control of said quarian homeworld (and in fact actively take steps to render it uninhabitable with their Dyson Sphere) when there is literally no physical barrier stopping them from doing so is the reason they face annihilation in the first place. They made themselves an obstacle, directly to the quarians and indirectly to everyone else via reducing quarian utility to the war effort, and later by actively and willingly assisting the enemy.
The geth are a race of software, and that "flawed" programming (which implies that the perfect geth is an obedient, stupid servant of the quarians - a sentiment that the quarians do, but the actual geth certainly don't share) what makes them capable of higher mental functions, like conducting psychological experiments, experiencing religion, wasting resources on restoring Rannoch (I wonder if the quarians could still re-inhabit Rannoch faster than making a new colony - their main reason for the war - if the geth hadn't did that.), and most importantly, having a strong enough wish of self-preservation to resist the quarians attempt to shut them down. Removing that would be like lobotomizing every human on Earth - even if their life would be sustained by outside means, their personalities, their culture, their worldview, their civilization would be destroyed. And the geth are little more that their personalities (individual differences) and worldviews, so this "reprogramming" would destroy almost everything they are, and reanimate their emptied shells with simple "intellingences" bound to the repurposer's will. You know who else does that? The Reapers.
Some loosely related thoughts:
- It was brought up that the geth are untrustworthy because they can be hacked. Except... the same applies to organics. There's indoctrination, enthrallment, and the Ardat-Yakshi's Dominate ability. The latter is not even Reaper-related!
- The logic of how the quarians decided to shut down the geth. As Tali explains it, when they realized that the geth showing signs of sentience, they were concerned that the geth will be discontent with doing their current, menial jobs. So what they did? Transferred the geth to more complex tasks? Asked them if they are content with their current jobs? Nope, the issued a general shutdown order. Cue war. Lesson: if it is intelligent enough to be able to object its working conditions, it is definitely intelligent enough to object its own death.
- Did the geth ever given a reason to give up Rannoch? As far as I know, the quarians never even considered the reclamation of the planet without destroying the geth first - even though the geth had little reason in staying on Rannoch beyond the convenience of established facilities. Even when the quarians had a trump card in their hand, they didn't tried to force the geth into leaving the Tikkun system peacefully - they just used it to hit them where it would hurt the most. And expecting the geth to hand over the greatest gift to the race that tried to exterminate them, waged a low-intensity war against them for at least the last two years, and considers them to be non-sentient, therefore okay to kill, brainwash, and to be experimented on; out of the goodness of their hearts, is the most entitled and morally myopic thing I ever heard.
- Rannoch is in the Terminus Systems, and the two major contender for it do not recognize a common authority above themselves. There is no independent legal system that could recognize their claims. But the de facto situation is that the geth inhabit and maintain the planet, and did so for 300 years.
Because geth decisions are entirely the result of mathematical and logical subroutines,
-That is only a fundamental difference from organic decisions if organics have souls in the ME universe. Such thing is never stated, and Cerberus' ability to bring back Shepard to life directs in the opposite direction. But it is consistent with the quarian's ancestor worship, so... congrats for in-depth roleplaying on your part?