Hi S.,
Protestants are called Protestants because our roots are from those who protested the Catholic church in the early 1600s. There were those within the Catholic church that were teaching things that were not found in Scripture. The common people did not have access to the Scripture so many in the Catholic church were not held accountable so errors were being taught (intentionally) and things like indulgences were collected. The Catholic church was VERY Christian before and they have given up a lot of that theology NOW that those protested many years ago. I do disagree with some doctrines that the Roman Catholics hold onto however I also disagree with some things that the Baptists, Methodists, Church of Christ, Lutherans, etc hold too as well. The crux for the Protestants in the 1600s was that salvation was by faith alone and grace alone. Many Priests of that time period taught that works gained you salvation.
There are other things like the additional books in the Bible that are not part of the Canon, praying to Mary, and the communion literally being the body and blood of Christ. I know many Christians in the Roman Catholic church and I know many non Christians in Protestant churchs. We grow, we learn and we move toward the truth if we truly know Christ.
If you haven't seen the movie "Luther" it would be a good watch. Luther was a devout Catholic...loved the Catholic church but saw their errors and tried to correct them from within the system. When he could not, he translated the first Bible into the common language for the people.
Hope this helps...
M.