How did New England become so secular and socially liberal?

[Mopsus]

Education.

I know this answer got dumped on, but it’s worth pointing out that Protestantism simultaneously asks its adherents to have an individualized relationship with God, and to put their faith in a set of scriptures that have been divorced from the authorities that traditionally underwrote them. It’s perfectly reasonable to believe that at some point, the dissonance became too much for affluent, educated New Englanders.