Is the joke bad taste? Yes
Did Will Smith laugh about it? Yes
Is it okay to hit someone over a joke? No.
But you are saying yes, because the joke is mocking his wife. Is that the line is it? that it is okay to resort to violence when a woman's hairline is the subject, what's next? all jokes banned? Because most humour comes from an element of truth, that's why it is funny. Someone will be at the firing line of it. The context here is the her illness is not a secret, the context here is that she is open about it, the context here is that she has previously said on social media that "they can make fun about it now", it being her baldness.
So Chris Rock did, and didn't even mention the illness, just a quick GI Jane reference.
But, what you are saying is that violence is fine when it comes to your wife's illness, one which she is open about it, one where she "invited" the joke herself.
Am I reading that right?