As I've mentioned above, I think you're talking about what I call "Puritanism", which is what I see Mr. MacArthur teaching.
Some might call it "Lordship Salvation" in that a person is mandated to perform at a certain level by the group, or they face being dismissed as
not being saved.
In other words, instead of practicing church discipline and putting people out of the fellowship for living in sin, yet treating them as a brother or sister...
they "go overboard" and pronounce that anyone who does not actively show themselves, by their outward works, to be saved, isn't.
I find that it's the same mentality as that found in other types of holiness movements...
Not that we should not be holy, but that some groups look at outward holiness as something that a person must do
right away ( instead of a work over time by the Holy Spirit ) in order to be considered as being saved.
This would put the Corinthians out of their own church, IMO.
Again, I think it depends upon the group and how they understand grace.
To me, grace is not only totally unmerited favor with God, it is also a patience that is extended towards His children that gives them space to repent, and doesn't come down on them like a ton of bricks for the slightest infraction.
Once again I agree with you here.
As I see it, the Reformers were very much legalistic and some could be rather unforgiving when it came to outward stumblings in sin.
As examples, I've read stories about John Calvin in Geneva and later the Puritans and how they treated their congregations,
especially in the Massachusetts Bay Colony and other places.
The feeling I get is that, while they seemed to understand
salvation by grace,
they didn't understand that the believer also
walks by God's grace, patience and kindness in this life.
Simply-put,
He does not rule His own children with an iron rod... even though He rebukes and chastens them.
It's done in love and a hand that only extends itself with regard to harsher measures when all methods of correction don't seem ( to us ) to be getting through.