For Nick, the game, basically, is convincing people. It's getting people to look at things your way. That's the big game in life, and that's what he's teaching his son. That's what he and his friends talk about when they get together. He's not defending cigarettes so much as he's defending his right to defend cigarettes.
All these people are so firm on their positions. That's where the humor in the movie comes from, ... It's like the debate team. Nothing is rooted, everything is malleable. As soon as you start to hate what Nick Naylor is saying, then you have a senator saying the same thing. Everybody is complicit; whatever their cause is, they all have unethical thoughts. It just shows that we're all just out there trying to ply our trade.