I used to think that we could not legislate morality, but then someone with a lot clearer thinking then mine set me straight.
If it is wrong to legislate morality then what do we do about laws that protect life? Thou shalt not murder is a moral principle that many of our laws are built around. Why is it illegal to speed? It isn’t because politicians are party poopers (well many are but that is beside the point). It is illegal to drive 100 miles an hour in a residential area because your chances of murdering an innocent person go way up when there are no traffic laws. We have laws that say you must go to school for a certain amount of years before you can practice medicine. The reason for these laws isn’t without reason. It is because when idiots practice medicine the chances of people dying go way up.
Thou shalt not steal is a moral principle, is it wrong to create laws to protect private property?
It turns out that most if not all good laws have a basis in someone’s morality. I am not saying that all Biblical laws should be made into secular law, a law forcing people to worship God would be a bad idea, because forced worship isn’t worship at all, it is acting. The trick is to recognize that personal freedom is a moral principle as well. While we can not divorce morality from the law, we do have to balance the idea of personal freedom, with the protection of others. One can not be free to murder, without taking away an innocent person’s right to live. One can not be free to steal without taking away another person’s right to private property. One can have the freedom not to worship, but they can not have the right of freedom from religion without taking away another person’s right to freedom of religion.
Smart Christian.net 
You bring up some good points, but I would argue that religion is actually safer when kept out of government. One need only to look to Europe to find religion blamed for things it is meant to oppose, like world wars or genocides. More often than not, those kinds of atrocities are carried out by governments (with religion attached to them). Here in the US, keeping religion separate will do a lot to keep it safe and vibrant.
Religion can be abused. And not all religions are good. But if there is no moral reason for a law it is a tyrannical law. If someone made it a law that you had to love Van Gogh paintings it would be a bad law. Why? Because I may question the taste of someone who does not like his paintings their is nothing morally wrong with not liking them. Those atrocities that you mention happened when people did not balance personal freedom with moral law. Taking the life of an innocent individual is wrong morally.
Hitler is often believed to be a Christian, but this is false. He used the name of God, because God had become a powerful political tool, but his beliefs were more in line with Darwinism then with Christianity.
He mutilated the Bible until it became anti-Jewish, but as any Christian knows you can not hate Jews without hating Christ. He wanted to create a super race which is a Darwinist belief. And as I am sure you know Darwinism is a very anti-religious system of beliefs.
The biggest atrocities of all time were not the crusades, the worlds greatest murderers were communist which outlaw religion. Once religion is divorced from politics the politicians go from trying to discover what morality is, to actually creating their own morality.
Joseph Stalin, Mao Zedong, Ho Chi Minh, and Pol Pot were the greatest killers of all time and they each outlawed religion in their government.
Who do you fear the most, people who think they will never be responsible for the evil they do if no man catches them, or people who think they will be responsible for the evil they do even if no man catches them?
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You say that our government is detached from religion but our very foundation for our government is
“We hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty and the pursuit of Happiness. — That to secure these rights, Governments are instituted among Men, deriving their just powers from the consent of the governed, ”
We are endowed by our creator. Who is our creator?
Our government was based on the idea that their is a moral standard created by someone who was higher then the King, but if God isn’t to be considered no one was higher then the King.