What many on the religious right do not understand is the importance of separating our church from our state. Throughout our history as a nation there have been people who try to push their personal beliefs into government dealings. What many of them don't understand is that in a free nation that allows them to practice their religion, it also allows others to practice what they want as well. I know it probably seems obvious, but our theocratic president challenges that notion.
The idea that our nation was founded as a Christian one is a myth, at best. Many of the founding fathers were deists or agnostic/atheists. Deism differs from theism on the point that God does not interfere in the lives of humans and does not dictate the workings of the universe. America is not a Christian nation, it is a free nation.
According to the CIA, America is about 80% Christian. Lets say there's a downward trend in religious beliefs over the next 50 years and that 80% halves to 40%, while atheism grows to 45%. In this scenario, atheists are now the leading "religion" in America. What if they tried and succeeded to enact that there shall be no acts of religion in America. They could claim that America was founded as an atheist nation (there's more of a case for that than this being a Christian nation) and that therefore God has no place within our borders. This may seem preposterous, but there's a reason why we have separation of church and state.
No one knows what the future of religious beliefs will be, but I'd rather live in a nation that kept religion entirely out of the government, rather than be force to believe what other believe. Religious freedom was so important that it was put right there in the first amendment to the Constitution. If you stifle one freedom, you begin down a slippery slope of endangering all freedoms. Therefore, I'd like to keep church and state separated, wouldn't you?