The game isn't subtle about it. There's Vellioth's skull, there's Spawn Astarion directly saying that we've broken the "cycle of violence and terror". It can't be more spelled out. In fact the scene with Astarion saying that strikes me as really badly written because he basically looks into the camera and says "This was about the cycle of abuse" which is goofishly blunt and not how a real person would talk.
I hope I don't get scolded for derailing the conversation but I have been thinking about this too again these past few days. I wonder if this strong, blunt emphasis on abuse was a later addition. Most of Astarion's story on his "good" path strikes me as overcoming his selfishness. In Act 1 he only cares about himself and uses the PC, in Act 2 he realises that he does not entirely like this behaviour and we slowly start to learn about his conflicting feelings towards what he had to do for Cazador, but he also learns about the ritual which eventually places him in a situation in which he has to choose between a very selfish action (condemning 7006 souls to eternal torture for his benefit) and recognising that other people are more than mere objects to be used. Cazador's abuse of his spawn is in this context just one facet of his selfishness, that was fostered by the environment he lived in, but it's just a part of a larger picture. He is exploiting everything and everyone and thinks only of himself - more than even Velioth, I'd argue.
It might be just me but the whole "I want you to live a life you can be proud of" and him being better than Cazador, the whole laser-focus on the abuse story, derails a bit from the things he learned about himself during Act 2, which is empathy.
In this context I also really do appreciate how the Gur are written, who are monster hunters but they aren't stupid monster hunters. The moment they learn that Astarion has the capability of being a person, they treat him like one. A monster isn't what you are but how you behave.
