... except that you're missing a whole bunch of subtleties, there. GRRM makes a point of saying she didn't physically or verbally abuse Jon, except in that one instance. What you missed is that raising a child in an environment where you make it very clear and they KNOW they're unwanted and someone less worthy than their half-siblings is a horrible thing to do to an innocent child.

But like you, most people don't see it as "abuse", particularly when it's of a bastard stepchild, which is why people in the novels don't view Cat as a bitch stepmother.