Flamestrike
Legend
Synthesizing a cure -- if there even is a cure, which seems extremely optimistic (we know how HIV works and it's taken decades to get as close as we have to a vaccine, with many more resources poured into it than they can in Last of US , even counting the dismal initial efforts in fighting AIDS in the 1980s) -- requires a lot more than what we see in and around that hospital. It's an incredibly fragile and resource-intensive process, including needing a ton of highly trained human beings, most of which have been eaten long before Joel starts shooting the remaining ones.
You're comparing a cure for a virus to a fungal infection.
Apples to apples.
Let's pretend there are still one million people living in what used to be the United States.
The purported cure stops people from getting infected (it doesnt cure the already infected as far as I can tell). Bites from infected turn from 'always lethal' to 'painful and annoying'. The infected can be safely hunted down and killed with far less risk than at present, and an encounter with one is much more likely to wind up with the human still alive.
No more people get turned into Zombies. The Fungus is on a one-way ticket to extinction.
The choice isn't between killing Ellie and a cure. It's a choice between killing Ellie and a remote possibility of a cure.
That's not the choice Joel has to make.
The choice is 'murder a bunch of people in a mass shooting spree, lie to Ellie, deprive her of agency and the choice she likely would have made herself, and potentially doom humanity - and millions of people - to the zombie apocalypse' vs 'leave her to die at the hands of the Fireflies, who might potentially be able to save humanity and millions of innocent people via her death'.
That's Joels choice.