Although I agree with Bioware giving fans the choice to be a d*** by making this particular non-decision and dooming the entirety of the advanced races, how could anybody make this choice, other than curiosity. The whole of the entire Trilogy is built around Shepard finding a way to stop this impending mass extinction, you're even brought back from the dead. To reach the point that you have spent three games to get to, be given several choices where everybody lives (they may not be the best choice, but at least we get to live), or do NOTHING and watch everyone die. NO. A thousand times, NO!
I did not get resurrected from the dead, help find a cure for the Genophage, end the Geth War, unite the galaxy and build the Crucible, "to let the Outer Rim burn for the sake of the Jedi teachings" (KOTOR II reference). This last choice betrays everything that Shephard has fought for, and everybody dies because of it. As Marvin the Martian would say "THIS MAKES ME ANGRY, VERY ANGRY!"