2+2=5

The song 2+2=5 is talking about people's efforts to convince others of untrue things.  For example, the lyrics say, "Oh go up to the king, and the sky is falling in."  Clearly, the sky is not falling in.  The tone is threatened, desperate, and defiant.  The theme is that the more untrue things are fed to you, the more you begin to believe them and question your own beliefs.  The last few lines back this up: "But it's not. Maybe not."