JAKE: This is not a tragedy. A tragedy is three men trapped in a mine or police dogs used in Birmingham.
BABY: Monks burning themselves in protest.
From the very beginning, we see Baby as a girl with different principles than, say, her sister, who's only concerned about shoes. Either that, or Baby's going to be the most annoying, preachiest girl in college.
NEILL: Are you going to major in English?
BABY: No, Economics of Underdeveloped Countries. I'm going into the Peace Corps.
We would argue that Baby can still use an English degree to change the world, but Baby wants to get in, get her hands dirty, and change things for the better.
BABY: You make me sick. Stay away from me. Stay away from my sister, or I'll have you fired.
It's cathartic when, later on, Johnny punches Robbie. But here we see that Baby's the first person to stand up to this jerk. It's incredible that someone so skinny has guts.
BABY: You always told me if someone was in trouble, I should try to help.
Baby isn't a born dancer, and odds are she wasn't magically born with her strong principles either. She learns to dance from Johnny, and it's her father who deserves a lot of credit for making Baby the honorable young woman she is.
JOHNNY: I've never known anyone like you. You see the world and you think you can make it better. Somebody's lost you find them. Somebody's bleeding and you…
BABY (interrupting): I go get my daddy. Yeah, that's really brave, like you said.
JOHNNY: That took a lot of guts to go to him! You are not scared of anything!
Johnny doesn't need any help moving his body, but Baby helps him move his spirit. Johnny admires Baby's principles, and he's been watching her to learn how to be a better man.
BABY: Why did you let him talk to you that way?
JOHNNY: What do you mean, and fight the boss man? […] Look I know these people, Baby, they are rich and they're mean. They won't listen to me.
BABY: Well then, why not fight harder, make them listen?
JOHNNY: Because I need this goddamned job lined up for next summer.
Once again, we see Baby's ignorance of reality rear its head. She believes Johnny should fight for what he believes in. Great. The problem is that Johnny doesn't have the privilege to fight. He's got way too much to lose. Only when Baby uses her privilege for good does she achieve change.
JOHNNY: Fight harder, huh? I don't see you fighting so hard, Baby. I don't see you running up to daddy and telling him I'm your guy.
BABY: With my father, it's complicated.
JOHNNY: I don't think that you ever had any intention of telling him. Ever.
Baby may be in over her head at times, but she is a good-hearted person with her head in the right place. When Johnny calls out Baby on her hypocrisy, she goes and changes it. No other baby can do that. Heck, most full-grown people can't even do that.
JOHNNY: I know you want Baby to be like you. The kind of person that does things to make other people look up to you. Dr. Houseman, Baby is like that, if you could just see…
JAKE: Don't you tell me what to see. I see someone in front of me who got his partner in trouble and sent her off to some butcher while he moved to an innocent young girl like my daughter.
JOHNNY: Yeah, I guess that's what you would see.
Baby's dad doesn't dislike Johnny because he's a crotchety old jerk. He has principles too. He believes that a man needs to take care of a woman he gets pregnant, which is an excellent principle to have. Unfortunately, Jake's directing his anger at the wrong person. His prejudices are getting in the way of his principles.
JOHNNY: Sorry for the disruption, folks, but I always do the last dance of the season. This year somebody told me not to. So I'm gonna do my kind of dancing with a great partner, who's not only a terrific dancer, but somebody who's taught me that there are people willing to stand up for other people no matter what it costs them. Somebody who's taught me about the kind of person I want to be. Miss Frances Houseman.
There's a possibility this speech is directed to Baby's father. Johnny wants him to know that Baby's exactly the type of girl that he would have wanted to her to be.
JAKE: I know you weren't the one who got Penny in trouble. […] When I'm wrong, I say I'm wrong.
Jake's apology proves that Baby got her principles from their father. When both of them see that they're wrong, they make it right.