They don't.
Mainline originally referred to the churches patronized by the wealthy people who lived out along the Main Line ~ a railroad that headed into Philadelphia in the early day.
A "mainstream" church actually doesn't have much cachet ~ you get outside the Roman Catholic church, which is the biggest Christian institution of any kind, all the others are quite small.
The RCC is the only MSM Christian church when you get right down to it.
So, what term do we want to use so that we don't needlessly confuse or insult our fellow Christians?
One radio host who has been popular on and off for years uses "Within the Pale of Christian Orthodoxy" ~ and that brings in just about everybody but not the Unitarians, Universalists, Mormons, one branch of Pentecostalism, and some other minor quasi-Christian offshoots.
I simply use "Christian" and you pick the meaning to see if it fits you. Best to avoid "Mainstream" and "Mainline" even if the particular usage is correct!
This appears to be NO problem for MORMONs. That is the group, headquartered in Salt Lake City, Utah, United States of America.
They religiously claim that ONLY their group has the RIGHT to call themselves MORMON.
Even though others manage to actually FOLLOW more MORMON scriptures than themselves, they relentlessly try to pound into the rest of the world's brain that the Big Boys Rule!
*The following is a letter from Elder Lance B. Wickman, General Counsel of the Church to publishers of major newspapers, TV stations and magazines. It was sent out on Tuesday, June 24, 2008.
Recent events have focused the media spotlight on a polygamous sect near San Angelo, Texas, calling itself the “Fundamentalist Church of Jesus Christ of Latter Day Saints.” As you probably know, The Church of Jesus Christ of Latter-day Saints has absolutely no affiliation with this polygamous sect. Decades ago, the founders of that sect rejected the doctrines of The Church of Jesus Christ of Latter-day Saints, were excommunicated, and then started their own religion. To the best of our knowledge, no one at the Texas compound has ever been a member of The Church of Jesus Christ of Latter-day Saints.
Unfortunately, however, some of the media coverage of the recent events in Texas has caused members of the public to confuse the doctrines and members of that group and our church. We have received numerous inquiries from confused members of the public who, by listening to less than careful media reports, have come to a grave misunderstanding about our respective doctrines and faith. Based on these media reports many have erroneously concluded that there is some affiliation between the two – or even worse, that they are one and the same.
Over the years, in a careful effort to distinguish itself, The Church of Jesus Christ of Latter-day Saints has gone to significant lengths to protect its rights in the name of the church and related matters. Specifically, we have obtained registrations for the name “The Church of Jesus Christ of Latter-day Saints,” “Mormon,” “Book of Mormon” and related trade and service marks from the U.S. Patent and Trademark Office and corresponding agencies in a significant number of foreign countries.
We are confident that you are committed to avoiding misleading statements that cause unwarranted confusion and that may disparage or infringe the intellectual property rights discussed above. Accordingly, we respectfully request the following:
Stated simply, we would like to be known and recognized for whom we are and what we believe, and not be inaccurately associated with beliefs and practices that we condemn in the strongest terms. We would be grateful if you could circulate or copy this letter to your editorial staff and to your legal counsel.
We thank you for your consideration of these important matters.
Sincerely,
Lance B. Wickman
General Counsel
We would be grateful if you could circulate or copy this letter to your editorial staff and to your legal counsel.
We thank you for your consideration of these important matters.
Sincerely,
Lance B. Wickman
General Counsel