I'd say you probably have been fortunate, but as always I can only speak from anecdotes about how Christianity usually works in the Bible Belt. From the point of view of the Pentecostal Holiness crowd, anyway. I think they're close to the most extreme on this view and look at most other denominations as a bunch of misguided wannabes at best and a bunch of dangerous people who are going to get a lot of people sent to Hell at worst.
People definitely get very bent out of shape over the legalism here, and being "holier than thou" is a real problem. I can't even say I blame some people for thinking like that when they believe the slightest unforgiven transgression will lead to eternal torment in fire. That's the kind of stuff that leads to people saying that drinking is a sin despite Jesus literally turning water into wine in the Bible, since drunkenness is a sin so you might as well not even take the risk. Or wearing jewelry, since that's vanity. Or men having long hair, because "god made man and woman separate" or whatever the justification is. Or going to Walmart on Sunday and buying a bottle of Mountain Dew, since that's desecrating the sabbath day.
So, you know, you do exactly what the Bible says, and take zero chances, because literally nothing is worth eternal torment in fire.
Except, of course, even then nobody can really agree on what's correct. Thankfully most people do still ignore large parts of the old testament, even the Pentecostals, but to be honest I don't know what their theological justification for that is. Obviously modern people are squeamish about a lot of it, and doing something like murdering a person because they're gay or worked on Sunday is also illegal, but I actually haven't met anyone saying that we should still do it because the Bible says so.
Anyway, I think one reason people fall into the legalism camp and trying to be "holier than thou" is because they want to be part of an exclusive club. It's part of human nature. They want to be better than their neighbors or competitors. They know the true way.