You don't see the big picture but I don't blame you, most people are short sighted.

After everything they went through I would have saved her. Maybe they can find another way to get the cure 

Well was there evidence that the vaccine would even have worked? I dont think so. So this is a though choice

So you'd choose to let your mother die. Got it. 

That shortsighted dig is deliciously ironic. 

I would have saved Ellie anyway. But the fact I was FORCED to do it infuriated me to no end and made me feel cheated on an otherwise magnificent game.

Dude, SPOILER!

He made the wrong choice because it shouldn't have been his choice to begin with. It was Ellie's.

Ellie. The fireflies already showed themselves to be desperate and there is no telling the power that a semi-terrorist group would have if they had a vaccine. They also don't have the means to distribute it far enough. The vaccine would just fuel more conflict between the government and the fireflies. The world is too far gone and as we've seen in TLoU 2, the world can rebuild without.

And ellie is just based as fuck. How could anybody kill her after going through that journey?

You're not thinking logically. Joel didn't make a choice. He wasn't confronted with a dilemma, consider the two options and 'choose' saving Ellie, he just reacting as a Father would (and should). He wasn't running and gunning his way through three rooms full of soldiers while simultaneously weighing the pros and cons. He was running to save his daughter, having already failed his first daughter. You're trying to retrospectively associate consideration to a situation in which there was NO consideration, not even the time to consider. 

When they were heading for the Fireflies, there was no indication that Ellie could die. Ellie herself spoke to Joel about what they'd do AFTERWARDS, meaning she didn't consider she may die. Ellie was then taken to the operation table unaware of what could befall her. There was NOTHING to consider, either from Joel's perspective or Ellie's perspective. The whole thing was just Joel saving his daughter from death. 

Only when he saved Ellie, went down the elevator and was confronted by Tess, was the consideration part of the narrative. At that point he DID make a choice but it was still a Father's choice and so the right one for Joel. The ironic thing here is the way they played this scene out. We see Joel's shoulders and head slump, giving the impression of 'consideration'. Because we, the player, saw that, when he's in the car and the camera is focused on a rather pensive looking Joel, for one moment (a deliberate moment) we think he may have chosen to leave Ellie. At that point, EVERY SINGLE let's player is hoping Ellie is in the back seat and then sigh with relief when she is. So, during the game, EVERY player believes Joel has made the right choice because we too now feel for Ellie.

It's perfect. All this 'I'd save the world' is primary school virtue signalling. 

Because the TLoU is not your story, it's the story of Joel and ellie. You're moving the story along, you're not making the decision yourself. You're forced to do it cause it's what Joel would have done, probably 10 out 10 times. If ND is telling the story of Joel, it wouldn't make sense for you to inject yourself at the last few minutes and retconn the story by making a decision that would betray Joel's new found paternal love for ellie. I could understand if the game had giving you multiple decisions to be made throughout the game AND then force you into one at the end but that isn't the case. Honestly, there was no indication that this last decision would be based on our input.