As for Will Smith: In his biography, he said he witnessed at 9 years old his father punch his mother in the head so hard that she fell and coughed up blood. That apparently affected him. He said that he felt powerless at 9, but now that he is older, he steps in to protect the women in his life. As for chuckling at first, he then turned to Jada, and after seeing the discomfort in her face, he went on stage. Now I am no psychologist, but it stands to reason that something went off in his head when he saw Jada’s expression, then he jumped in to defend her honor.
That story is tragic, but it doesn’t come close to justifying his actions here. Chris Rock didn’t punch Jada told a bad joke which offended her and Will Smith ought to have responded with words when he was accepting his award. Called Chris out and made him see the pain he had caused with his joke. That would be defending his wife’s honour. Instead he escalated the situation with violence and in that moment Will stopped being the powerless child and became his father. I’m sure something went off in his father’s head too and the result was his mother coughing up blood. I don’t think we should be defending Will for following that path.