Would it make sense to say a phrase is taken for granted? IE Oftentimes children take the phrase "that's not fair" for granted.
I don't think so. I think people (mostly kids, but not exclusively) say "that's not fair" or "you wouldn't understand" by rote, without understanding how redundant and meaningless those phrasings are.
You might say people say those things without thinking, when they need an excuse for something but don't want to explain themselves!