In reference to The Crucible, particularly Act I, I think we see the desperate need for separation when it comes to the deliverance of justice. The affliction or problem starts in the Rev. Parris' home. He is so scared of what's going to happen that it seems the problem perpetuates itself and he looks for a way out. This play does point out a time when maybe the state overstepped their bounds, not the church which we think oversteps its bounds more often than not.
For today, I would agree with the above answer but would add that many people cite the references to a Creator in "The Declaration of Independence" and "God" in other founding documents. This acknowledgment suggests that most people respect a moral code that the church provides. What I value about how we have things organized today is that a person can believe what they want to believe and are free to worship the way they want to. I would keep things just the same.
In my opinion, we do a pretty good job of striking a balance here in the United States right now. I think that governments should not be a reflection of the dominant religion in their society, but I do think that it is not fatal to have some acknowledgment of religion.
For example, I would hate to see a government in which religious leaders get to make all the laws. I do not want to go back to a time when you couldn't have your store open on Sunday, for example. I would not want to have my kids being taught someone else's religion in a public school.
On the other hand, I have no problem with the idea of using the word "Christmas" in a school. I don't mind calling it "Christmas Break" or a "Christmas Program." I think there is nothing wrong with acknowledging that most people in the country are Christian as long as we don't force others to do anything serious in the way of having to adopt Christian beliefs.