In God We Trust

Okay, so I was checking out a twenty dollar bill and realized the "In God We Trust" on it. What the hell is going on with that? They take it away from everything else and leave it on the freakin' money? Yeah, I know - it would cost a lot to drag in all those dollar bills and replace with new ones. So I'm wondering what the hell do "they" think it is costing to take God out of schools, public buildings, etc.?