Pretty sure I would if it came down to a binary decision but the world doesn't work like that, it necer would and the closest being would be a serious of progressively narrow choices however in the case of Ellie it's not about killing humanity. It's a small hope of a potential cure for a better world and you bet your ass anyone close to me is not getting sacrificed for that. It's the equivalent of throwing someone into a volcano for better weather and crops but with science behind it.
Not really. Ellie was immune to the disease. There was evidence to show that she could help people from becoming "zombies". Plus its what she herself wanted.