Law /
Weapons laws in Poland. Carrying a concealed handgun? [918]
Firstly you have the extreme groups like those amongst the Mormons who practise polygamy
They're not fundamentalist Christians, many theologians wouldn't consider them to be Christian at all (they call themselves Christians but many disagree) they have some seriously weird rituals like the veil ceremony (filmed in secret and now available on youtube I highly recommend watching)
And mainstream Mormons no longer practice polygamy (there are some very small rebel offshoot groups that do but they're not officially Mormons)
The Amish also have had under age sex scandals.
Also not fundamentalist Christians. In the US context 'fundamentalist Chistian' refers almost exclusively to evangelical groups devoted to ideas like literal interpretation of the Bible, being 'born again' as an adult, tithing etc)
And crucially evangelicals have some influence as a voting bloc but no real power in practical terms. I agree there's lots of crazy on the fringes (like a group that wanted/s to base the legal system on the bible) but they have no chance of exercising real power.
Just bear in mind that America produced the Ku Klux Klan
A couple of different times, but IINM they reached their membership peak in the 1920s (slight revival as an underground terrorist organization in the civil rights era) but they've been close to having anything like real political power, racist institutional power in the South had other foundations and heavily depended on setting blacks and poor whites against each other...