A character thinks their loved one is okay even though they're obviously *beep* and gets really close to them... One of the characters is infected but hides it from the others... I think these scenes have been perfected. Let's see some new ones!
It may seem stupid but it's one of those human characteristics that would probably be difficult to overcome if you were in the same situation.
The average person probably wouldn't want to admit that their loved one is gone, especially when they're right in front of them, still moving. Naturally, you're going to want to try and save them and hope that there's a cure or there's another way to bring them back. When it comes to an emotional connection, logic can go out the window and even though everyone they saw get infected ended up the same way, there's always that thing in the back of their mind saying "...but _____ is different, they won't end up that way."
Not only do you want to deny that they're infected, but once you accept that, you have to admit that there probably is no cure and you have to let them go. Even though it's a cliche and I will continue yelling at the screen saying "(S)HE'S INFECTED, YOU MORON, GET OUT OF THERE" I can understand why it happens.
Why not? Most relationships are of broken people in some way --- some are WAY more broke than others. The convict says about ?? Wagner char -- "firecracker" - she reminded him of his recent ex.