The season finale of The Last of Us aired this week, so if you haven't seen it (or played the game), watch out because there'll be SPOILERS ahead!
The episode started with Joel and Ellie bonding and feeding a giraffe, before Joel got clocked in the head. He woke up in a hospital, and there was Marlene, telling him that they were about to operate on Ellie in order to attempt to essentially extract the cure from Ellie's brain, killing her in the process.

Naturally, Joel thinks that's a terrible idea, so he goes on a video-game-style (natch) killing spree through the hospital, murdering dozens of Fireflies and also killing the doctor who was going to supposedly make this cure.

Joel kills Marlene and takes Ellie away, and he lies to Ellie and says that raiders attacked the hospital, and that there are tons of other people with immunity like Ellie.

At the very end of the episode, Joel doubles down on that lie, swearing to Ellie that he's telling the truth... which Ellie appears to see through.

Some people feel Joel was selfish and even kind of a monster for what he did, viewing it as a way for him to put a Band-Aid over his trauma from losing Sarah.
joel sleeping peacefully knowing he lied to ellie just so he could have a sarah do-over #TheLastOfUs
You gotta admit, if you were living in that horrible post-apocalypse where living through any day isn't a given, you didn't know who Ellie was, and you were told that taking one person's life could save all of humanity... you'd probably consider that a fair trade.
Whether it would have worked or not was never the point, because Joel didn’t know either way. In his own mind, he still picked Ellie over humanity, killed innocent people, then lied to her about it for years. https://t.co/8kQ5QPS3O9
But plenty others pointed out the flaws in Marlene's plans. Who is this doctor they have? There's never been a vaccine for a fungal infection, and you're telling me that this guy is not only a good enough surgeon to perform this brain operation, but he's also able to synthesize and mass-produce something that's never been done before? Using medical knowledge and technology from 2003? They're all just willing to kill their ONLY subject/specimen — a walking medical miracle — to do that?
I know the story is fictional, but I’m still trying to make sense of why they’d need to remove Ellie’s whole entire brain to create a cure. That “doctor” Marlene found may have been a total quack. Team Joel all the way. Fuck them Fireflies. Marlene was a moron. All due respect.
And let's not ignore the fact that Marlene decided it would be best to not ask Ellie for consent at all. Sure, supposedly it was so that Ellie wouldn't be scared, but you gotta wonder how much of that decision was fear that Ellie would say no.
marlene saying "it's what she'd want" when they were never planning on waking her up and asking themselves