I'm not sure why people are so shocked. I imagine if you took 100 couples and had someone crack jokes about the wife suffering from alopecia (or any other health condition that caused hair loss) I'm not sure how many husbands would take it all too well.
I might not take it well but I am old enough and mature enough to know that I wouldnt walk up to the person and hit them. At 53, Will Smith really should know better that the response to a comedian on stage cracking a joke at the expense of another isnt to go and smack them in the face. If it was, Al Murray, Stewart Lee, Micky Flanagan and almost every other comedian on stage would turn into royal rumble contests