But it is a game, so why would you try to say that it's not? What possible agenda could someone have to try and exclude games that aren't exactly like the kinds of game that they already like to play?
Hobo, I don't think anyone is trying to oppress you or others by defining "game." However, I cannot be in a discussion and permit game to mean absolutely anything. Therefore, it behooves you to admit there might be limitations on what can rightly be called a game, because a word only has meaning if that meaning is shared between the people communicating. As has already been pointed out, game already has a lot of history within the RPG community as taking a certain form, and in the wider world, games have various definitions and connotations that bear on what we would consider a roleplaying
game. Unless you use the definition of game as being "something frivalous," virtually every definition involves amusement, purposeful activity, challenge, and surprise.
Further, although there are various definitions of tabletop RPGs, they all come to general agreement on the vast majority of games. The further you depart from those shared premises, the more likely you are to not meet someone's definition. At the point at which an RPG is played in a fashion that the most logical result is not permitted, you have errored for virtually any RPG.
Playing a scene, with a beginning and a foregone conclusion, could be a game, but it's not a roleplaying game, because in a roleplaying game, a character has full freedom of action. If you wanted to be really picky, you might call it a role-taking game, but honestly there is little reason to call it something other than a storytelling game, or improvisation. If, for instance, the Joker's defeat is a known destination, then you are playing an improvisational storytelling game in which you determine how that occurs, using dice or whatever as aids in play. However, Batman's player is not really roleplaying, except in the most literal sense of playing a role, like an actor. The player is not inhabiting Batman, but rather, inhabiting a playing space. At the point at which you have two co-authors writing a story, you are not playing a roleplaying game.
The moment logic is allowed to triumph over the framework, you have restored meaningful choice to the equation. Being literally unable to change the course of Normandy because they are not capable still leaves the players in full command of their characters.