I may read denominational literature about the faith but, because of the Holy Spirit's presence in me and a constant study of Scriptures, I usually know whether or not the teaching is Biblical. It has the "smack of truth" or I sense something is off, it doesn't sound right. Now some people will mock me saying this, thinking I am boasting or depending upon my own personal interpretation of Scripture, but I think you may agree that it is definitely NOT what we are saying. Jesus said he would send the comforter, the Holy Spirit, and he would lead us to all truth. I do not think it was only meant for an elite few, but for all who belong to God through faith in Jesus Christ. So like you said, there were many people outside of denominational divisions and were simply born-again Christians.
If more people studied the Word in a prayerful and humble way, allowing the Holy Spirit within them to illuminate the truths of God's Word, they could avoid much of the false teaching that is out in the world today. If Christians assembled together with those of like mind and hungered together for the truth, God would lead them to it. Pastors and evangelists are great, don't get me wrong, and God uses them in mighty ways, but we must all be responsible for learning the Word and not just swallowing whatever we are fed by others. We are to search the Scriptures to know that what we are told is true or not.
So why then did Christ establish a Church to spread the Word if we are expected to get by solely on our own interpretation?