Through sin, Martin Luther and others broke away to kind of do their own thing and started to bring God down to a human level as seen through their eyes in humanism.
Martin's sin or the Pope's? I can see how you could see it that way. The Pope of his day and several before him were very corrupt. They failed to follow the teaching of Jesus. Martin was not bringing down God to a human level, just the Pope. He was not looking to replace him. He was wanting the church to repent. It did not. It may not have still. (as far as I know, being boring is not a sin.)
Instead of proper teachings and interpretation, you get a lot of self taught mixed up people out there.
Yes it true, you can lead yourself astray by leaning on your own understanding, or even scholarly instruction. There are a lot of lost people believing some crazy stuff just because they were told that or just plain tradition. You will not be led astray by the Holy Spirit. He is the only accessible authority in God. Ignoring him is to ignore Christ. Replacing him with another doctrine (esp. a human one) is idolatry. If you mean a proper guide being a subordinate to a corrupt Pope, Bishop, Priest, then I take the Holy Spirit any day.
I said what makes them a valid Christian anyway despite their running around headless is their accepting of Jesus Christ as their Lord and Savior for their salvation.
So there are no saints outside of the Catholic Church. Sanctification doesn't occur without the Pope. Is that what you are saying? You can get saved and that about it. (Sounds Baptist to me) Without a man's authority on Earth, nobody has ever been sanctified. Is that what you believe?