Here are my thoughts as promised. Most of them have grown out of my experience as a professor and lecturer. These fears are fears that have been voiced over and over by people in my classrooms and audiences.
Non-canonical texts make us uneasy because:
1. They are are unfamiliar. Their stories, sayings, and mythologies are not what most people today are used to. In so many ways, they are different from the canonical story that is known and loved so well by Christians around the globe.
2. They made many of the "fathers" of the apostolic church uneasy. These fathers, many of whom are "saints" in various church traditions today, are recognized authorities (like the Pope). If they didn't like these texts or think them valuable, why should we?
3. Many of the non-canonical texts reflect expressions of Christianity that people today do not want to practice. Who wants salvation dependent on giving up marriage and sex? This might have been attractive in the ancient world, but not so much today.
4. They give us pause to ask questions of power - its use and abuse. This is a source of discomfort and guilt for those in power. For the powerless it is a very fearsome and paralyzing reality. Why did only certain forms of Christianity survive? The question has a multifaceted answer, but the use and abuse of power is part of the equation.
5. They force us to face issues of selection and legitimacy, issues which challenge faith doctrines like "biblical inspiration," "biblical inerrancy," and "apostolic succession." Why do we have the stories of Jesus that we have, and not the others?
6. They bring an element of doubt into reconstructions of Jesus. If we have to take into account the non-canonical material, the Jesus we have in the NT gospels begins to have some competition. So it's trying to sort out the question, "Will the real Jesus please stand up?" that brings discomfort.
7. They are written later than most (but not all) of the New Testament texts. So there is less confidence extracting history from them - although most scholars remain confident about extracting history from canonical texts, even though these stories are graced with virgin births, feeding miracles, walking on water, healing miracles, visions of the dead on high mountains, and the pinnacle of all, the physical resurrection of Jesus. How are these stories any different from the young Jesus making clay birds and clapping his hands, bringing them to life?
8. When we study the non-canonical texts (and the patristic witnesses about them), we realize that so-called "heretics" like the Ebionites were far more similar to the very first Christians than Irenaeus was. If one's Christianity is based on understanding oneself as emulating the first Christians, this is a problem.
9. They suggest that the second century of early Christianity is important, as important as the first. Why? Because it is the period in which Christianity was thoroughly engaged in the process of normation. The forms of Christianity known today are indebted to that process.