It wasn't the fact he roughed Terra up. It was the fact he got so bloody angry and out of control with it. That isn't Slade. Also, the thing he beat her over was just PATHETIC! Slade kicking the hell out of her for running awa? Oh yeah! Real manipulative! That's REALLY going to win her to your side, isn't it!
However, when he was fighting Robin, it wasn't out of raw anger. It was self defence really, Robin started the fights, Slade defended himself and taught Robin some "manners" along the way. He didn't become this angry, raging monster when Robin smacked him in the face... yet got so annoyed over Terra not following an order? Yeah right.
I'm sorry, Say what you like, I just can't stomach Slade's reasoning in Aftershock. He was perfectly fine until part two, where he just became a slimmer version of sabertooth or something.