After all, as a few sectarians did, if your fate is already decided by God, you may as well have sex with as many people as you can and lead a life of earthly bliss. It makes no difference regarding your predestined outcome. But the Puritans, whether Presbyterian or Independent, were a joyless sort. Yes they believed in religious liberty for themselves but not particularly for others, as the early American colonists showed, and those that had a more parish outlook (and accepted that there were collectivities of Christians) expected parishioners to behave. Only later did a capitalistic middle class adopt liberty for Jews and Catholics too as a way of breaking the power of the Anglican soaked feudal regime.
Unitarians forget what a relief there was in the population when the Restoration took place, to bring back some fun into ordinary life as well as a bit of the old naughtiness among the upper classes. The Restoration then involved juddery movement to trinitarian tolerance simply because a rising merchant middle class was, to some extent, connected with early nonconformity. The cat had been out of the bag a little too long. And then the Restoration itself found its limit when James II was overthrown.
Well there is an answer to why they were so joyless and showy in their piety including over others in this perceptive interview about the legacy of Calvinism in Wales:
RTE: What is 'Double Predestination'?
Fr. Deiniol: The Calvinist doctrine is that God has predestined people from before the creation of the world for redemption. 'Double Predestination' is the belief that God has predetermined and preordained not only who shall go to heaven, but who shall go to hell. In other words, He has brought some human beings into existence, having already determined that they shall go to hell for eternity. They maintain that He has done this in His infinite Wisdom and that the logical contradiction between that and God's infinite love is not for us to question and understand. So, the God of love becomes, in their theology, a tyrannical and arbitrary monster, whose excesses are far worse than the worst tyrants of human history, who only tormented people for a limited period of time. The God of Calvinism creates some people in order that they should suffer for eternity.
RTE: And this not only severs any notion of free will, but I imagine that you would have to take care to appear "good" to prove that you are one of the saved, or is that too simplistic?
Fr. Deiniol: No, that's very accurate.
"How do we know who is saved?"
"Oh, by their fruits you shall know them."
Accordingly, observable behaviour becomes very important, and at a certain stage in the evolution of things, when conviction and faith are no longer so strongly present, this preoccupation with appearances becomes a very distinctive characteristic of these societies. That is certainly what I think happened in Wales. Also it means that people don't look at the darker side of themselves, and don't encounter their shadow. Darkness is then projected onto other people, so you have groups that are the scapegoats, the lowest of the low.
So one can imagine that as the Puritan-Presbyterians slipped into Arminianism, the importance of showing piety maintained itself, and formed a kind of spiritual and intellectual elitism. Then, within these chapels, a sort of biblical and early scientific/ technical capitalism and intellectual elitism took hold with its 'in the Bible' unitarian ideology as a sort of theological takeover from within the dissenting academies and among the trustees.