How did New England become so secular and socially liberal?

[Former President tack50]

It was my estimation that the religious fervor itself created a generational friction that wore away at such fervor over time.

So basically too much puritanism and religion led eventually to an "equal and opposite reaction" backlash?

That makes sense and is an interesting theory. The question is then why hasn't that happened elsewhere (like say, the rural Southern US, which are just as religiously strict nowadays?)