The early Protestant leaders stepped out boldly against that man both Catholics sin, the universal Roman Catholic Church. They brazenly defied the antichrist’ power and stood firm for the idea of Sola Scripturia. That is the bible and the bible alone over man or church as the rule that we are to live by.
However, being of the homo sapiens family made them sinners. The Catholic religion had mixed an awful lot of paganism in it’s teachings that it became an impossible task for any one person to bring out all that the bible has to teach. It is here where Protestantism became domed to failure.
They started to persecute Catholics but they also placed themselves upon the ground of persecuting their fellow Christians who were seeking nothing but sola scrtptura in their service to their Savior.