Then you fell for the narrative tricks ND did. You make Ellie do certain things when you play as her. Now compare to what you do as Abby when you played as her. It comes across very one sided. ND wants you to like her despite her past.
(was this vague enough not to do a spoiler tag? I hope so)
I guess that is one way to put it. ND tried to do something different here by showing that there are always two sides to each story, but apparently they didn't pull it off quite well, judging by people's reactions.
You know, it always bothered me (and disturbed me) the fact that so many people were not only okay with what Joel did at the end of Part I, but kept seeing him as a "hero" after that. So I suspect ND's plan this time around was to see how far they could take Ellie before people realize that there is something wrong with these characters.