Common sense doesn't always win out when you're angry. And there really needs to be a different word than "assault" when it's a slap or the like. Assault makes me think that the victim was brutalized, not that their cheek might be a little red.
I get punishing him for stepping out of line, regardless of how justified I think he might have been, but did he really do something worth a firing? Especially considering the not exactly "professional" history of WWE, it seems a bit hypocritical to me.