1. All non-canonical texts are Gnostic.
2. Canonical texts are early while non-canonical texts are late.
3. The non-canonical gospels are not "gospels".
4. The writers of non-canonical texts were hostile toward canonical texts.
5. Extant versions of non-canonical texts are their autographs.
I have noticed these same assertions in my own reading of this literature. I must say it really gets my ire up. I would go even farther than Tony does here. These are not just faulty arguments, they are powerful fallacies that are trotted forth in the literature as "truth." Particularly whenever I read material written on Gnosticism by apologetic scholars, I find myself gritting my teeth, since their concept of Gnosticism is as old as the hills. Not only is it not current, it is a regurgitation of the kind of older scholarship that was written ages ago, rediscovering the early Church in terms of modern Protestantism.
I look forward to Tony's next five.
Update: Friday 13th of July
Michael Bird responds to Tony here.