Is this some sort of remnant of evangelical puritan protestant ideology?
I don't understaun this.
If you ask me, it'd make as much sense as Orthodox and Christians.... or Shia and Muslim...
I know not all Christians are Catholics but for feck's sake...
They're all Christians to me....
Edit:
It's a U.S thing but this is the sort of things I hear...
https://www.gotquestions.org/Catholic-Christian.html
I am a Catholic. Why should I consider becoming a Christian?
I now know more distinctions (apparently Catholicism requires duty and salvation is process, unlike Protestantism?) but I still think they're of a similar branch (Christianity) so I just wonder the social factor
We're talking about "orthodoxy" here. Wikipedia
In Christianity, one of the first creeds established was the Trinity; God is the one God in three persons: Father, Son, and Holy Spirit. How that works is a mystery unlike anything existing, although we try to illustrate and make parallels.
This is a sharp dividing line for calling anything "Christianity."
Muslims honor Jesus as a prophet, but that does not make them christian, because they deny his deity. Mormons do not believe in only one god (ultimately), or in the Trinity as one, but instead separate see this link.
Both Catholics and Protestants believe in a true Trinity.
As a former Mormon, the Trinity issue always seemed like a bogus distinction. I'm sure you can find plenty of sects you would label "Christian" that also believe God the Father and Jesus are separate, distinct entities