Even many inclined to support Will Smith are troubled by his initial reaction, laughing, before he could have seen Jada's anger. Trying to put myself in his place, one usually goes along with the MC, whether it's a roast or flattery. Perhaps he turns to see Jada's reaction, then realizes what has passed before stepping up to smack Rock. Obviously the better response would be perhaps a thumbs down & calling Rock out—he sat close enough.

I think another issue is how the ceremony was laid out. Normally there's a stage fronting regular rows of seats. Even sitting in the front row it would have taken Smith longer to reach the stage, given him a moment to cool off & rethink. Perhaps next year the Academy with restore the more traditional layout.