Owen Gleiberman Chief Film Critic Religion, Karl Marx said, is the opiate of the masses. Today, he would likely say that the opiate of the masses is fame — the desire for it, the things you have to do to get it, the fragmentary nature of it (the old “15 minutes” is now, in many cases, more like 15 seconds), and everything it’s supposed to bring you. The new fame, the lusty fickle kind bred by social media, is at the center of “Wild Diamond,” a startlingly bold and true French drama that premiered today at Cannes.