It shows good faith. It shows your willingness to negotiate. You can go through life upset that the world doesn't work the way it "should" - you can even refus

It shows good faith. It shows your willingness to negotiate. You can go through life upset that the world doesn't work the way it "should" - you can even refuse to participate like the original poster. But you will generally have a worse outcome, so is it worth it? Why not play along, just a little? Same thing goes for: dressing up (why should it matter if I'm in a suit?), sending thank yous (why should it matter if I already said thank you?), and just about any other social grace.