Dr. Octopus
Footballguy
I think it's obvious Ellie became a surrogate for his lost daughter and he couldn't stand to lose a second daughter for "the cause". His first daughter was shot down for no good reason - just to slow the spread - and the same could very well have happened here - since they didn't know if the "cure" would actually work.I think his decision was entirely based on his guilt for not saving his daughter and has almost nothing to do with Ellie