Monte Obsessed? I don't think so!
Dr. Midnight, you say MC has an unhealthy fascination with evil. OK, let's look at the "evil" products he's produced.
DMG? Not evil
BOEM I &II? Not evil
Demon God's Fane? No more evil than any other high-level adventure produced by either WotC or another d20 publisher.
Call of Cthulhu d20? OK, evil. Or at least scary enough to be called evil.
The Banewarrens? OK, evil.
Book of Vile Darkness? Yes, evil, evil, evil!
Now let's look at those three products. Both CoC d20 & BoVD are Wizards products he had already started while employed at WotC. When he left, all the projects he wound up having to finish his projects as a freelancer (read his message board posts, website articles, and interviews with Morrus).
Did he choose to do them? Well he's a huge CoC fan by his own admission, so he probably jumped at the chance to do a d20 version. But the product itself was created by Wizards & Chaosium, not Monte.
Yes he pitched BoVD to Wizards. He also pitched a Book of Exalted Deeds. If you read his interviews he thought instead of class splatbooks (Sword & Fist, Song & Silence, etc.) that Wizards should try something new and go for alignment splatbooks. Didn't pan out that way, but Wizards dug evil. So again, he wound up doing that.
The Banewarrens, the least evil of these three (OK, I haven't seen BoVD, but I the title alone makes it more evil than the Banewarrens). I own it. It's not that evil. And it seems to have been an adventure he designed to run his victims-I mean players-through.
Add to that the facts that in one of his interviews he actually said he was looking forward to NOT doing any more evil products, and how they just kind of snowballed up on him, I'd say that adds up to proof that he's not obsessed.
Simply put, you're so wrong, ignorant, and out of line you owe Monte Cook an apology.