I wonder if Michael Afton even knows that Vanessa was stabbed by their dad?
I don't get the impression that he ever visited her in the hospital when she was in a coma. It could be that he just didn't show up for her, or it could be that he actually didn't know.
I could see this eventually leading Michael to finally question whether his dad's approval was worth it or not. But I feel like his first response would be denial.
I think he would accuse Vanessa or whoever was telling him about it of lying. Then he would try to justify it with some nonsense like "He did it for her own good" or "It hurt him more than it hurt her." (total bs obviously)

