Now, the Long War against Gnosticism in the Catholic Church is an ongoing thing, dating back to before the fourth century throwdown and continuing today. Gnostics are all about the division between the impure body and the pure mind, common knowledge and hidden knowledge, and other dichotomies that the Church is on record as denouncing. Fundamentally, though, the real problem with Gnosticism is that it divides Truth (and therefore salvation) in two parts, the public Truth that everyone gets from the Gospel and the secret Truth that can only be revealed to those special people who can be trusted with the Mysteries. This directly contradicts what we know about the ministry of Jesus, who hung out with all kinds of folks and spread the word about the new covenant not just to the Jews (who had been defined by the first covenant as the Elect) but to everyone that was around at the time, whether they were Gentiles, Jews, Samaritans or whatever. Jesus wasn't passing out the secret password to the chosen few, he was shedding his blood for everybody. Gnosticism says you have to know the secret word to get into Heaven; Jesus says you can't get to the Father except through Him, which is no secret at all. Put another way, Gnostics put a limit on God's grace, and as we all know from Sunday school God has no limits.
Now, as to the books Athanasius and Irenaeus excluded from the canon, the apocrypha: there was and is no argument that those books could not be read. IIRC, nobody ever put them on the Index, though in the early days of the Church many warned against the possible confusion that could be caused by these books, and Leo the Great went so far as to call for them to be burned.
So while Cobb may find the apocrypha of interest, I think he's a little late to the game. Pretty much any alternate version of Christianity you could want is out there already, including some that deny the divinity of Christ. Which makes one wonder why they're even bothering, but that's their problem, not mine. Studying the apocrypha may yield things of interest and possibly some insights, but you have to remember that they're like tail fins and spoilers - accessories that aren't necessary (much less sufficient) to the proper undrstanding of the faith.