It was not Scriptural adherent Christians that killed Roman Catholics, it was Rome that killed Scriptural-adherent Jews and Gentiles (Christians) long before Roman Catholicism existed, and Roman Catholicism was a tactic that Rome employed to gain control over all things, even the church of God. Rome employed the way of Baalam, which is domination via infiltration. Rome could not destroy God's church outright.
Despite its persecutions for years, the numbers of Christians continued to grow. People dying for their faith, and the evilness of Rome was apparent. God still preserved the remnant of His people even during the reign of so-called Holy Roman empire, and Scriptural adherent Christians existed long before -- the protestant movement - which was caused when Martin Luther posted the truth everywhere - so the truth was out regardless if Rome killed him. But Rome merely jumped on the bandwagon of Protestantism, creating its own cults... as to keep people bound in confusion. Not just ecumenical movements - but major cults are founded by Freemasons - such as Charles Taze Russell of the Jehovah's Witnesses, Ellen G. White of Seventh-Day Adventism, Joseph Smith of Mormons (Latter-Day Saints), and Mary Baker Eddy's Christian Science religion.
The Vatican rules through its Orders: the Knights of Malta, the Jesuits, the Freemasons ... these are all long arms of the Vatican. For those in the know, they know the Vatican rules behind the scenes, and it has ruled for years now, but it ruled through secret societies for years to keep protestants in the dark, because Protestants/Christians were a much larger populace. People used to have more awareness of the Bible and the differences between it, and the other religions -- but they just don't teach this stuff anymore, and it tends to be filtered through secular humanism when it is spoken of.
Kind of long, but I recommend the watch, if you want perspective: