Ditko's prose style doesn't really lend itself to excerpts, as you can see above, he constructs amazing, sometimes maddeningly complex arguments. So I encourage you go order the newsletter in question (or join me in encouraging Ditko's co-publisher to put together a collection of the relevant essays).
However, a few tastes:
"So certainly, the GG [Green Goblin] could hardly be any reason for me quitting Marvel"
"Now digest this: I knew from Day One, from the first GG story, who the GG would be... I planted him in J. Jonah Jameson's businessman's club." [prior issues of the newsletter had a contest to identify all the planted appearances of the character]
"I planted the GG's son (same distinct hair style) in the college issues..." [referring here to Harry Osborn]
This will probably be my last reply here, as the commenting system here makes no sense to me. Feel free to contact me via e-mail or my site (should be linked in my name above) if you wish to continue.
Just in case this is unclear to anyone reading this, it was widely believed that making Norman Osborn the Goblin was entirely Stan Lee's initiative - this completely debunks that myth too. (An unnamed man resembling Norman Osborn was indeed seen in Jameson's business club in ASM #23 and #25.)