From January 1973: Watergate, Roe v. Wade, Vietnam, and the Month that Changed America Forever by James Robenalt:
...even a top leader of the United Church of Christ labeled [the Supreme Court’s decision on Roe v. Wade] ‘historic not only in terms of women’s individual rights but also in terms of the relationships of church and state.” The clergyman’s reasoning: “Although religious principles often form the basis of secular law, we hold that where religious beliefs vary, American law traditionally establishes the neutrality of the state. The doctrine of one religious group is not imposed by legal fiat or enforced by criminal sanction on the rest of American society.”
There’s the rub.
The Religious Right believes that that one religious group does get to impose its doctrine on the rest of society.
And they don’t believe religious beliefs vary. There are no religious beliefs. There is only belief. Belief in the one, true God. Their God. So there is belief and there is godlessness. They are the believers. Everybody else is godless. And the godless have no religious liberty because they have no religion. So the only religious liberty that needs to be respected by law, custom, tradition, and practice is their own.
Right Wing Christians do not understand the phrase “religious liberty” as meaning that individuals have the liberty to worship as their beliefs and consciences dictate, anyway. When they say the United States is a Christian country they mean it’s a country in which Christianity rules. Their brand of Christianity. They are the only true Christians. Their “religious liberty” is the liberty to tell everybody else what to believe and how to conduct their lives, and whenever they are blocked from doing that, they feel their liberty threatened.
In their mouths “religious liberty” is just a synonym for "us" or “we”. So they’re not saying “religious liberty is threatened.” They are saying “we are threatened.” It’s another Right Wing “Us versus Them”-ism. And the majority of Americans are them.