In videogames, you play against your own competence or against other players. The one which shows the most mastery at the game win. The goal of the game is competition.
In simulators, you get to do something you could not because it would be too dangerous to attempt in reality. Driving a race car, an airplane, a train, ship, etc. The goal of the game/simulator is to procure an experience otherwise impossible or not convenient.
I didn't get to play a lot of Postal. I don't remember if it was the first or the second but I remember the developers saying "it's a life simulator, the game doesn't require you to kill people. If you kill innocents, it's your own choice." Kind of hypocrite to give player guns and nothing to shoot. I guess Postal ain't a game, it IS a simulator: a civilian killing simulator.
Let the game developers do what they want, but when they produce tasteless crap like Postal, don't support them. God damn, even GTA was a fucking masterpiece compared to that postal crap. And I don't like GTA.