That's the scene I would refer to in a GF IV storyline which would feature Anthony changing his mind about being in the "family business" after the murder of his sister.

We see at an early age that Anthony really did have a desire to follow after his father, but in the years between GF II and III Kay has worked to suppress that desire in him.

Becoming an opera singer is about as far from the "family business" as you could get, but seeing a traumatic event such as Mary's murder (and the attempted killing of his father) might cause something inside Anthony to snap and he could become obsessed with vengeance and power.

And he would also come to realize, "Every time I think I'm out, they pull me back in ..."