[2020] Why is team Rainbow fighting itself?

Am I wrong to assume that every operator in the game is part of Rainbow 6? If so, why are the team members killing each other? That we play as both the defenders and the attackers in the few single player situations leads me to believe both sides are on the same team. What's the context of the multiplayer matches?

Was there a fracture in team Rainbow where all the defenders decided to go all terrorist? If I had to make a theory, I would say all of team Rainbow is trapped in some sort of Operator Valhalla where they square off with each other for eternity before returning to their mess halls for mediocre pizza and coffee.