Alright, I finally made time to sit down and type this out.
I find no problem with doctrinal books and the sermons of men in their nature. I, in fact, find them to be rather helpful and insightful in many ways. I come in conflict with my conscience when men take and study these human works to the extent that it takes away from God's word. I even have seen some study exclusively the writings of others concerning God's Scriptures.
How can we in good faith do this and ignore the command to study for ourselves. The Bereans whom Paul ministered to were not just content to hear one of the greatest evangelists of all time, one of the apostles of Christ; they took his teachings and then studied God's Words to really see what God's will for them was. All men will make errors and mistakes in their own interpretations. If we then take this flawed writing or sermon as our guide, we will, like all humans, make errors and misinterpret that teaching, so that now the flaw is multiplied to twice its original magnitude.
Think of a carpenter building a house. If he cut's trusses or supports for a roof. If he uses his pattern to cut piece1, then uses piece1 as the pattern for piece2, the flaws and misshapeness of the first piece will be multiplied in the second. But if he goes on to cut piece3 using piece2 as a pattern then that flaw will be even greater. After all the pieces for the roof are cut in this manner, the carpenter may be short of supplies, and the pieces will not fit together properly, and so with the body of Christ.
The Church cannot function when all the members are believing and basing their beliefs on another person's flawed thinking. God's word has only one meaning, and the closer we are to that meaning, the better we will be able to live together without disagreements and the discord that comes from a disunified Church.
"All scripture is God breathed...." God spoke these words in our Bible, indirectly though they often are. This scripture is our only insight into the mind of the All Powerful, All Knowing God. We need to make sure that we are not deceived in any of it. We must study on our own, and take lessons from the great theologians, who have studied more than we, but we must always compare these teachings to the original scripture for accuracy.