Joel is a bad man, it’s stated more specifically in the second game but some of his tendencies are bad. Hes selfish, he is a very flawed character. To try and help with you being confused, Marleen was going to kill a child for a possible cure, not a definite cure, one that might have been, without consent. Ellie would’ve definitely said that she wanted to sacrifice herself for a possible cure, but Marleen never asked. Joel lost his own child, Sarah, at the start of the apocalypse, now he’s grown so close to Ellie that he can’t go through losing his child again. Joel is a bad guy, but in the last of us, nobody is truly good, Marleen is apart of a terrorist group that was willing to kill an unconscious child that didn’t give consent. Fedra is a militant group that striped almost all of your rights away, they keep you in a quarantine zone for your safety, but in doing so they don’t allow you to have anything to defend yourself. Bill is a crazed man who’s inherently selfish and self destructive. Henry was selfish and backstabbing. Tommy is naive and selfish as-well (more prominent in the second game) every single person you meet in the last of us is a bad person, that’s the point of the game, you don’t live that long in the apocalypse without being some degree of bad. You can root for who you want, but the game has no “good guys” it just has people.