If you believe MacFarlane, and others who think like him, sex is a sort of competition between men and women. Whenever women engage sexually with men–for instance, by appearing topless in a movie that is viewed by men–the man “wins” and the woman “loses.” In the video, the women whose boobs MacFarlane says he saw are portrayed as shocked or embarrassed, whereas Jennifer Lawrence, whose boobs MacFarlane notes that we have not seen, is shown to be celebrating.
In this view, women have no agency to experience sexuality on their own terms and for themselves. MacFarlane et al. do not realize that a woman might want to appear topless in a movie not (just) to be viewed by men, but because it makes her feel good or because it increases her opportunities as an actor, or for any other reason.