This post will be explaining why the separation of Church and State is absolutely vital to the American government- but in order to do that, everyone needs to be on the same page, which begs the question: what exactly is the separation of Church and State? The separation of Church and State has three main tenants:
The government shall not favor one religion over another in any meaningful way: This means that, for example, the government cannot give tax breaks to Christian churches, but not to Islamic mosques.
The government shall protect the freedom of religion of its citizens: The government must protect the ability of its citizens to practice a religion of their choice to the best of its ability, until the practicing of that religion causes an obvious harm to others. For instance, blood sacrifices are illegal, even though they are sometimes religiously mandated, due to the harm they cause.
The government shall protect the freedom from religion of its citizens: This means that the government must ensure that no one is required by law to obey any religious mandate purely because it is religious- in practice, this means that the government cannot outlaw bacon because Allah says so, but it can outlaw bacon because bacon is poisonous.
The Christian perspective
So, what is the alternative to a government with complete separation of Church and State? A flawed/untrue Theocracy. A true Theocracy is basically Bible times Israel. What happens to the country, how it fares, its successes and failures, are all directly cause by its relationship with God. An untrue Theocracy is any form of government in which the ruling person, or legislative bodies, or family, or whatever claim to have direct divine inspiration from God- and make policy based on what 'God' tells them to do. This form of government- the untrue Theocracy- ultimately violates all three tenants of Separation of Church and state, as they are rarely- if ever- truly divinely inspired. So, why should Christians care about these tenants?
The government shall not favor one religion over another in any meaningful way
This is admittedly the least important tenant from a Christian standpoint, however it is still very important. Why?
Not upholding it opens the door to religious prosecution (no guys, Christians are not already being prosecuted. That's ridiculous). Once the Government decides to make concrete policy that treats Christians better than Muslims, or Hindus better than Jews, or any religion better than any other religion, that is religious prosecution. I hope I don't have to explain why prosecution is bad. Actually, if you're someone that doesn't understand why prosecution is bad, you can go ahead and get off my blog, because you need to go crack a history book. Or any book, really.
The government shall protect the freedom of religion of its citizens
I'm going to ignore all the arguments for freedom of religion in and of itself here- instead I'm going to talk about why forcing Christianity is unbiblical, does not create more Christians, and belittles God- why a mandated Christianity is counterproductive.
First, mandated Christianity defies the example of God. Throughout the Bible, God/Jesus calls people to him, tells people to obey, to be righteous, etc- but it is never forced. Jesus never forced obedience to him. Why? Christianity is all about true repentance and love. The government can't do that. The government doesn't have this magic bottled morality that it can make people repent and come to Christ with. At best, the government could force people to pretend to be Christians out of fear, which would only cause those people to grow angry and resentful at the Christian faith. It would alienate the very people it hopes to save.
Second, God directly speaks on freedom of religion, and advocates it: But if serving the Lord seems undesirable to you, then choose for yourselves this day whom you will serve, whether the gods your ancestors served beyond the Euphrates, or the gods of the Amorites, in whose land you are living. But as for me and my household, we will serve the Lord. (Joshua 24:15 NIV)
Finally, mandated Christianity diminishes God. The government passes one simple bill, and the U.S. is now a better country, somehow a more Christian country. That is the mindset of a Christian theocracy. It doesn't work. One can’t seal up magic Bible juice, sprinkle it on the constitution, and fix America. The idea that the government can convert people, the idea that God somehow needs the government to punish people for not worshiping Him. This idea that God somehow needs the government to help him with his religion... This idea is wrong, and is borderline blasphemy!
The government shall protect the freedom from religion of its citizens
For the Christian perspective, every argument for freedom of religion applies here as well. Morality enforcement is bad- it is contrary to the Bible, creates false morality, and diminishes God.
The secular perspective
One could write an entire book on this, which I do not intend to do. Instead, I'll only be going over one or two strong arguments for each tenant.
The Government shall not favor one religion over another in any meaningful way
Violating this is the first step towards a Theocracy. It is important that a government recognizes each religion as equally valid or invalid, lest it pass policy based on a favored religion. I'm pretty sure every Atheist can agree with me- Theocracy bad.
The government shall protect the freedom of religion of its citizens
First and foremost, this is a freedom of opinion/belief issue. Religion is a very intimate and personal belief choice, that ought to shape one's entire life. For the government to attempt to regulate or mandate your very beliefs is a violation of Human Rights, and indeed rather Orwellian.
Second, historical precedent shows us that not protecting freedom of religion is bad. In the middle east we can see that a lack of religious liberty only results in bloodshed- as we can see in ancient Rome and Egypt. Look, guys, this never turns out well, mkay? It is worth noting, however, that religious freedom/liberty only goes until it does harm. There's a reason we don't let cults sacrifice virgins on grounds of religious freedom.
The government shall protect the freedom from religion of its citizens
Both arguments from the above point apply here. In addition, the violation of this tends to infringe on the other two tenants- you're not going to simply force someone to have a religion, you're going to force them to follow a specific religion.
I intend to do a followup post on this topic once someone like Ted Cruz starts yelling about how we need to uphold Christian values and blah blah blah.... But, until then, this encompasses the main points of separation of Church and State, as well as the main reasons it should be upheld, particularly from a Christian standpoint. I didn't put a lot into the secular section of this post, as I'm pretty sure all Atheists can agree on this one. Perhaps if I see something that suggests this needs further elaboration I'll do a followup post, but I find that unlikely.
Next I'll probably write about, hmm. Maybe welfare? Or global warming? Or maybe I'll try to find the most recent stupid thing said by some presidential candidate, and do a post on that. We shall see.
Anyways, thank you to the three people that read this, and if you have any disagreements with my points, feel free to comment or message me.