Madison's argument is the most straight to the point. The Thirty Years' War ended in 1648, so just 150 years prior to the Founders writing America into existence, and being former British citizens they well understood the constant turmoil of rivalry between Catholic/Protestant/Anglican/whatever in England. So they just agreed that they wouldn't have any of that bullshit in their government, which has worked fantastically for everyone for the subsequent 249 years.

You can see the depths of their wisdom on this issue when you look at the burgeoning "Christian Nationalists" and see the little tremors of division between them along Orthodox/Catholic/Protestant lines. The more excited ones seem to be Orthodox/Catholic but the grand weight of bodies is on Protestant already. If any of these people were to somehow actually seize the power of the state, would they not immediately re-open the wars of religion by mandating that their particular denomination of Christianity become the official religion of the USA, forcing every other denomination to war? They're all plotting and jostling each other to open the exact floodgates of brother wars that the Founders wisely preempted by writing the 1st amendment.

Christian Nationalism isn't just anti-American, it's retarded. And this is all ignoring that the main driver behind this "movement" is Hispanics who want to be included in White Nationalism but found out that being "White" in Mexico isn't the same as being White in America.
>Oh I'm not invited? Uh well...maybe religion should be our unifying principle. There's Catholics up here right hermano?