I’m a direct descendant of Anne Hutchinson, so definitely knew about Puritans not encouraging heresy.
To get back to the original question from way back when. What happened with Evangelical Christianity is what happened to everything else. The 60s. (Actually it started before that, but the 60s make a good enough breaking off point.) Prior to the 60s, Mainline Protestantism was the dominant religious force in America and Mainline Protestantism was much more conservative than it is today, but still relatively liberal in its outlook. Well, let’s back up a bit.
Beginning in the late 1800s as the Third Great Awakening was winding down, there was a pretty serious rift in the Church united and particularly in the American Church as to how to deal with a world that was increasingly non-agrarian and increasingly more social rather than communal in aspect. The church largely began moving toward more liberal stances and developed a number of Modernist Theologies that eventually led to very liberal theologies that we still use today. These theologies apply Enlightenment philosophical thought and scientific discovery to Traditional Christian theology and you end up with something not too different than what United Methodists or Episcopalians or most Mainline Protestants believe today. Unfortunately, the Third Great Awakening had brought a lot of people into Christendom though that we’ll say were less amenable to such things. The Modernist movements were largely the work of very educated very wealthy people and they were academic and dry and not necessarily particularly appealing at an emotional level.
New people brought in by the Third Great Awakening as well as Southern Americans were not satisfied with this mainstream Academic trend (whom Southerners saw as dominated by Northerners) and they fought back. They created a new Theology that they called Fundamentalism. It was essentially an idea that regardless of whatever new discoveries or evidence we get, there are certain fundamentals which are necessarily true. There have actually been a number of these ‘fundamentals’ over the years, but they typically center on Biblical inerrancy and the literal account of the Bible (although in the beginning, fundamentalists would NOT have said the Bible is literal, that came later.) Needless to say, in Mainline Christianity, liberalism won fairly easily and within 15 years of Fundamentalism hitting the Academic circuit, there was not a single mainline Protestant seminary that taught it.
In Evangelical churches though, things were different. Evangelicalism arose out of the Second Great Awakening and gave us such hits as Jehovah’s Witnesses and Mormons. It was a time of serious religious revival, particularly in the frontier and for whatever reason the Burned Over District. Basically, there was a serious religious fervor that took hold of the country, particularly among Methodists (who later became mainline, but we’ll get to that.) As often happens in these movements, there was a bit of an Apocalyptic element and the idea that as many people as possible needed to be saved from the pits of Hell. So you get people traveling around holding revivals and camp meetings and all sorts of things to try to convince as many people as possible to repent of their sins and start living the good life. The abolitionist movement certainly aided in this and lent credence to the idea that the world was in serious need of saving. Basically, this is the start of Evangelicalism.
One of the hallmarks of Evangelicalism was its focus on the people on the outskirts of society. Evangelicalism for all of its faults in the beginning was extremely equal opportunity and was really at the forefront of social justice. Groups like the Salvation Army got their start as Evangelical groups. They really felt that they needed to reach the poor and destitute that society had forgotten about. This causes lots of problems down the road and honestly it’s why we’re where we are today, but we can get to that as well. Prior to Evangelicalism, the poor weren’t particularly cared about by pretty much anyone. Church was not something for the poor. The poor were working not attending services and there were roadblocks to get into churches like pew rental fees. Evangelicals thought that was serious bullcrap and you ended up with denominations like the Free Methodists who abolished fees for churches and particularly aimed at converting the poor. Evangelicals were responsible for the blue laws that closed down workplaces on Sundays and were instrumental in the early labor movement. So anyway, what’s important to remember is that Evangelicals actively courted the poor and so largely became comprised of the lower classes.
So hopefully, you can see what’s happening. These mainline churches and movements that are largely comprised of wealthy, educated Northerners have become bastions of liberal theology (We still are! Go us!) Evangelical churches which which largely consisted of poor, lower class southerners and minorities, rejected this and became increasingly fundamentalist. What’s important to note though is that largely it didn’t matter. Evangelicalism was largely looked at perhaps the way that we look at the Black Church today - they do their thing, it might be a little bit different, but it doesn’t really matter because by and large the vast majority of people were mainline and went to their Lutheran or Presbyterian or Methodist churches and the Baptists and other Evangelicals were just a group of weirdos from the south that could be safely ignored.
Then, we get Baby Boomers who basically suck and ruin everything that they touch. What began happening in the 1960s was that Boomers had largely decided that they had enough of organized religion. They decided that organized religion was for schmucks and the Beatles and Timothy Leary had the right idea and you see young people start to leave. The people that left though were largely white, wealthy and educated - which was the exact group of people that dominated mainline Protestantism. So all of these white, wealthy educated people start to see their white, wealthy educated spawn drop out of the church and it causes a crisis. People start asking themselves, what the heck is going on? They look at who is leaving and it’s basically the sons and daughters of the people who are advocating a very liberal theology. Meanwhile, they look at Evangelicals who aren’t having that problem at all. They’re actually growing and some mainlines go “Here’s what happened, we embraced these liberal theologies and people abandoned us.” From here, you actually start to see movement from mainline churches towards Evangelical churches. This encourages their worst tendencies. During the 70s and 80s, Evangelicals are slurping up disillusioned mainlines and mainlines are getting absolutely hammered from both sides. Conservative mainlines are becoming Evangelical and liberal mainlines are dropping out of Christianity completely.
Evangelicals figure, “Hey, the problem is that these liberal ideas are killing Christianity, we need to fight these ideas or else we’ll become mainlines.” (To be fair, they aren’t wrong.) So they get these new influx of converts who are generally wealthier and increasingly better connected and people begin to take the fight to the political sphere. We end up with groups like the Moral Majority who are actively supporting conservative candidates. Mainlines on the other hand have lost their moderating voice and are increasingly seen as irrelevant while Evangelicals essentially take up the mouthpiece of Christendom. As they gain power and prestige, they become more and more associated with their political wings. This encourages people on that side of the political spectrum to join Evangelical churches. Eventually what we see by early 2000 is that liberals are essentially persona non grata within Evangelical churches, so you end up with a sorting effect. Mainlines were able to recoup some of those disillusioned liberals, but largely they have just left the church. What this does to Evangelicals is that they see attendance fall and they are going through the same crisis that mainlines did 40 years ago. Their response though is to look back on their history and say, “Why were we successful then?” “Because we were fundamentalist and conservative.” Instead of saying, “Why isn’t that working now?” They are saying, “We need to become more fundamentalist and conservative. We know that becoming liberal makes you die like the mainlines have, so the only other option is to go further right and further fundamentalist.”
So, the long and the short of it is that it’s really Baby Boomers and Millennials fault that Evangelicals are the way they are. If you actually managed to read this tome, I hope you learned something.