Logic problem: The founding principles of the U.S. and Christianity.

[The Grand Nudger]

They want it not so other creeds can stand as equals to them, they wanted so they can pursue their own agenda of atavistic dominance without scrutiny from other creeds.

Right, "atavistic dominance" in the sense of "trying to persuade other people to agree with them". At least for the overwhelming majority of Christians. Remember who Jefferson wrote the "separation of church and state" letter to. It was a religious group, and Jefferson was trying to reassure them.

Personally, I don't see anything in the Bible telling me that I should oppose the First Amendment. I'd note that the approach Jesus, his apostles, and the various other New Testament evangelists took was not to advocate for coercive government action, but to talk, persuade, teach, and minister. If there's a good argument that the Biblical model of conversion is coercion, I'd like to see it, because the notion strikes me as plainly false.

Christianity is coercive, even if those advocating it do not intend to be. Sadly they often do, and so I can list just about any sort of distasteful coercion you care to imagine as being leverged in service of the christian faith. These are terrible things done by terrible people, you might say (which would be true). Neverless, had these people merely preached the gospel without taking any action whatsoever they would still be leaning heavily on coercion by fear and ignorance. So you can take your pick between the evils done, or the evils inherent, but either way, it's coercion.

Or any of the more specific examples from american politics recently.