> To be honest I really dislike this kind of vague speculative fearmongering when targeted at specific minority groups, which seems extremely dangerous. It historically blends right into overt bigotry and sectarian oppression.
Basically, I'm repeating the contention of sociologist Eric Kaufmann's book Shall the Religious Inherit the Earth–that in the long-run religious (ultra-)conservatives will dominate due to high birth and retention rates.
It isn't "fearmongering", because that assumes one is presenting a takeover by religious conservatives as negative. One might view it as positive. One might view it as neutral. I'm not presenting any value judgement of it here.
The contention isn't about any religious group in particular, it is about ultra-conservative religious groups in general. Ultra-Orthodox Jews happen to be the clearest example of the phenomenon, but there are other candidates – Old Order Amish, Latin Mass Roman Catholics, Salafist Muslims, etc.
Personally, I doubt ultra-Orthodox Jews will ever single-handedly takeover America, because in the scenario I am talking about, there will likely be other (non-Jewish) ultra-conservative religious groups, with which they'll share power. But I do think it plausible that in 2 or 3 centuries from now, North America will be a much more reliigious and much more conservative place than it is today. Not certain, of course, but plausible.