It's just a nasty double standard that roots back to basic ideals. Because way back in the day the stigma began that men were stronger than women, it became ironically funny to have a woman beat up a man. But of course, it's never funny the other way around because of the apparent reality of the strength difference. However, these ideas are continued to this day to the point where it's taken WAY too far. Now we have characters like Sam who horrible abuses Freddie and makes his life miserable, and we're all supposed to laugh at a bullied kid. And of course, the moment he slaps back people are up in arms.