I watched something similar recently and I don't understand why it's so difficult for atheists to concede this point. I'm happy that Jesus argues for separation

I watched something similar recently and I don't understand why it's so difficult for atheists to concede this point. I'm happy that Jesus argues for separation of church and state ("Render unto Caesar") and I don't need to find a non-religious inspiration. There are many examples of Christians coming up with good ideas. The fact that they did/do means very little in the debate regarding the existence of God.