I seen this thread and I decided to read the two pages of posting thus far.
DSM you bring up a good point regarding false teachers and the false teaching that have infiltrated the catholic church.
The subject of false teachers is addressed extensively in the New Testament.
Jesus address this subject in Matthew 7
13"Enter through the narrow gate. For wide is the gate and broad is the road that leads to destruction, and many enter through it. 14But small is the gate and narrow the road that leads to life, and only a few find it. A Tree and Its Fruit 15"Watch out for false prophets. They come to you in sheep's clothing, but inwardly they are ferocious wolves. 16By their fruit you will recognize them. Do people pick grapes from thornbushes, or figs from thistles? 17Likewise every good tree bears good fruit, but a bad tree bears bad fruit. 18A good tree cannot bear bad fruit, and a bad tree cannot bear good fruit. 19Every tree that does not bear good fruit is cut down and thrown into the fire. 20Thus, by their fruit you will recognize them. 21"Not everyone who says to me, 'Lord, Lord,' will enter the kingdom of heaven, but only he who does the will of my Father who is in heaven. 22Many will say to me on that day, 'Lord, Lord, did we not prophesy in your name, and in your name drive out demons and perform many miracles?' 23Then I will tell them plainly, 'I never knew you. Away from me, you evildoers!'
and in Mark 13:22
For false Christs and false prophets will appear and perform signs and miracles to deceive the elect—if that were possible.
Also see Acts 13:6
They traveled through the whole island until they came to Paphos. There they met a Jewish sorcerer and false prophet named Bar-Jesus,
and in 2 Corinthians chapter 11, Galatians and the book of Jude, 1 Timothy, and 2nd Peter along with the first 3 chapters of Revelation
Historically the Christian church has had to deal with several false teachings along with mystical pagan practices and traditional Jewish traditions that were present during the days of Jesus. From the early days up to the 1500's there were many illiterate people and copies of the bible were mostly in Latin and very scarce, so for the average person did not have the opportunity to read the word of God.
Going back to the 1500's it was Martin Luther who through his studies of the Bible and teaching came up with his 95 issues he believed the Catholic religion contradicted with the Holy Bible.
Here is his 95 theses
Here is a synopsis of his history