When I played the first time, I feeled like Joel, I needed to save Ellie at all costs. I entered the room, the surgeon then hold up the scalpel, and I used it against him, I left the other surgeons and took Ellie.
To me, humanity is the one who destroyed everything. To me everything comes back to the intro scene. It wasn't an infected who killed Joel's daughter, it was a soldier, a human. Other humans did the worse things to others too. Joel spent 20 years living among these people. He knew what humanity have become. He lost faith in people until he met Ellie. Important is the fact that he saw how his brother and its people were rebuilding society despite the infected. Maybe he thought there was another solution without sacrificing Ellie. To me the real cure was recovering society and civilization to work together against the infected and not just something that "probably" could prevent the infection, because nothing guarantee Fireflies would use the cure to good use either....
And nobody questions the fact that the Fireflies didn't ask her for permision. In some point, in the Univerisity in Colorado, you have an extra scene between Joel and Ellie discussing how they think the cure will work or what the Fireflies will need from her and they say that probably only a blood test will be necessary. Of course Ellie would help if only her blood was necessary, but I don't know if she would have agreed if she needed to sacrifice herself.







