As a conservative, I certainly affirm what the First Amendment says, namely, that “Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof.” I am in no way an advocate of official state-sanctioned established churches with government-paid clergy, and I don't want to have civil rulers prohibit members of Catholic parishes, Unitarian churches, or Jewish synagogues from exercising their faith — though precisely that was happening in parts of colonial America.
I strongly suspect that won't answer your question, so let's clarify my answer with the original intent of the founders.
John Adams wrote that “We have no government armed with power capable of contending with human passions unbridled by morality and religion ... Our Constitution was made only for a moral and religious people. It is wholly inadequate to the government of any other.”
Seems pretty good to me.
Let's take a look at the views of another Founding Father who, in addition to being the primary author of the Declaration of Independence, was a governor of Virginia, then one of the most powerful states. Perhaps especially important for this purpose, Thomas Jefferson was the author of the Statute of Virginia for Religious Freedom, probably the most “liberal” of the colonial documents on that subject apart from the two historically tolerant colonies of Rhode Island and Pennsylvania.
Jefferson had certain views about homosexuality. He was the head of a committee which wrote this law: “Whosoever shall be guilty of Rape, Polygamy, or Sodomy with man or woman shall be punished, if a man, by castration, if a woman, by cutting thro’ the cartilage of her nose a hole of one half diameter at the least.”
http://www.monticello.org/site/research-and-collections/bill-64
I think I might argue that Jefferson's penalty for homosexuality could perhaps be modified to be a bit less harsh, and I think I might argue, contra Adams, that an atheist can be a good citizen of America, but Jefferson and Adams give pretty clear indicators of how the Founding Fathers would have applied their views of religious freedom to our current discussions in modern America.
In this regard, I ought to add that Jefferson was a Deist and Adams was a Unitarian. These were two of the most religiously liberal Founding Fathers.
If castrating homosexuals and saying atheists can't be good Americans is included in the proper “original intent” definition of religious freedom, I think it's pretty obvious that modern Americans use the words "religious freedom" very differently from what the Founders meant.
I've given you facts which show pretty clearly that America today has greatly changed from what the Founders intended. You may think that change is good, and to some extent I may agree with you. What you can't do is argue that my views are something out of line with the Founders — except that they might consider me to be too liberal in my views of what should be tolerated.