You guys are very forgiving of this kind of deception. Do you really think that Burger King's supplier threw in a little horse meat as an added "luxury" bonus for its customer? Of course not. It's a filler, which suggests there's all kinds of other shit in there. Not to mention that it's probably not the finest cuts of horse.
When you buy a hamburger, it's a reasonable expectation--in the West at least--that it's going to be cow beef or, if its not, that they'll disclose that it's some other meat.