A few things.
1. She wasn't his daughter. She was his assignment.
2. Humanity was at risk. The needs of the many outweigh the needs of the few. Don't you Star Trek?
3. He had to lie to her. If his actions were noble, he could let her decide.
- 4. In saving Ellie, Joel killed several people. Doctors who were just doing their job. Who made the decision to do what was best for humanity. Joel killed them without hesitation.
Would I sacrifice my adopted daughter? I have a real daughter and, for the greater good, I'd sacrifice myself for them. If she grew up and joined the military, I'd respect her wishes and I'd understand why she would be willing to risk it all. I understand that Joel lost his real daughter at the beginning of the game and maybe he saw Ellie as someone who could fill the void but, in the end, he was selfish. He didn't even give "his child" an option.
1. True but you can still care an awful lot about that if she is pretty much one of the few people which doesn't want to murder you for recources.
2. Is humanity really worth saving though.
3. Do you think a 14 year old Child is capable enough to make such a decission and understand the impact of such a decission. Also Firefly never mentioned the failed trials to extract a cure from tissue from immune persons. Neither did tel the truth in that regard.
4. Technically speaking you did kill them. Since you could get what you want without killing them.
4. No, I had to kill them. I was bloodlusting or something. I couldn't stop myself!