Which was to counter the massive proliferation of threads bashing many non Catholic belief systems.
What Catholics call "Protestants" or "Prods" or "prods" and "separated brethren" got tired of the constant denigrating of their denominations and so started posting threads exposing the non-Scriptural non-Biblical aspects of the teachings of Catholicism.
Some examples being that if you are baptized Catholic (by the way, no one is "baptized" into any denomination) you are "marked", ie that is branded, for life as a Catholic and you stay a Catholic all your life and you cannot leave to become a Christian instead.
Also that to be saved and go to heaven everyone must "come back" to the OTC (One True Church) or they are not legitimate Christians and are not part of the body of Christ.
Apparently Catholics complained about threads from legitimate sources explaining the misdirections perpetrated by Catholicism and OTC's were admonished to not post those threads anymore.
You talk about the nicknames for non-Catholics, there are equally offensive nicknames for Catholics that I have seen here.
One is RC — there are many rites in the Catholic Church, but only one church. The rite referred to with those letters is the Latin Rite.