Freedom FROM religion – where the people are free to believe as they wish – or to be free from faith altogether – absent coercion from government, absent punitive measures by government, and where theists are prohibited from using government to compel adherence to religious dogma.
It's known as the Establishment Clause of the First Amendment, found in the US Constitution.
How do you get "freedom from religion" from "free exercise thereof"? It's freedom of religion, which of course includes the right to follow no religion at all.
You sound like you want to force atheism on all the believers in the public square, such that they can only freely practice religion when they're cloistered away in the dungeon of their home or church.
That is not Constitutional.