JayDizzle
Let's Go All The Way...
Again, it must have something to do with other choices you made, because it was clear to me the options I needed to choose because in my Paragon run Legion sacrificed himself to make each Geth independent, and afterwards the Geth and the Quarians agreed to work together to build a better Rannoch and live on it together.
Rannoch Ending Spoilers AND the available outcomes/how to get them*:
*i.e., don't click this shit if you ain't there yet...
ME Wiki and it's contributors said:Aftermath
The shooting has stopped, but not the yelling. Legion and Tali square off. Legion wants to upload the Reaper code to the geth collective, as it enhances their processing functionality to the point of achieving true intelligence. Tali is naturally fearful of what this might mean for her people, whom the geth were able to shred when they had these enhancements. Shepard must navigate the decision.
Your first choice is to allow the upload, or to let the geth die. By choosing to upload, a second decision branch is opened: allow the upload again, stop Legion, and a Charm/Intimidate check ("Rally the fleet" / "Warn the Fleet".
■ If you allow the upload twice, Legion will will sacrifice itself to distribute the new programming and the upload will be finalized. The Migrant Fleet will be destroyed to the ship by the newly-enhanced geth. Tali will join her people, casting herself off a cliff; there is a Paragon interrupt, but even with it you will not be able to save her. Shepard will gain the geth as a War Asset, but Tali will no longer be selectable as a squadmate.
■ If you choose to stop Legion or choose to let the geth die at the first decision junction, Legion will attack, forcing Shepard and Tali to kill it. The quarian bombardment annihilates the geth completely. Thereafter, the Migrant Fleet joins as a War Asset.
■ Passing the Reputation check, which allows the Charm or Intimidate option, is the most difficult, though also the most rewarding, as it leads to the quarians and geth co-operating. The quarians will back down, and both fleets will join as War Assets. While Legion is forced to dissolve his 1183 runtimes to disseminate true intelligence throughout the geth collective, he achieves true sentience and individuality first, and is able to accept Tali's friendship before passing.
Note: There are so many factors contributing "under the hood" to the Reputation check that, as yet, no confirmed equation exists for calculating whether your personal saved game will pass muster. However, the fandom's best understanding of the matter as follows:
First, there are factors which seem to be binary; failing any one of them is believed to immediately flunk the Reputation check:
■ Shepard must have at least four bars of Reputation.
■ Tali and Legion must both be present.
■ The player must have imported a save from Mass Effect 2.
Afterwards, there are more factors which build up Shepard's trustworthiness to both parties. Players are believed to be required to have done at least some of the following:
■ Destroying the heretic geth in Legion: A House Divided. (Rewriting them is thought to have no positive or negative effect, though it is possible that it does in fact have a negative one: Legion will mention in post-Priority: Geth Dreadnought shipboard conversation that the rewrite increased the number of geth who supported the decision to appeal the "Old Machines" for help.)
■ Preventing Tali's exile in Tali: Treason.
■ Brokering a peace in the Tali/Legion post-loyalty conflict.
■ Completing Rannoch: Admiral Koris.
■ Actually saving Admiral Zaal'Koris vas Qwib Qwib, instead of allowing him to sacrifice himself for the sake of his crew.
■ Completing Rannoch: Geth Fighter Squadrons.
Bioware made damn sure to make this a "Damned if you do, damned if you don't..." choice.
Much moreso than...
The end of the Tuchanka missions