No –repeat NO– fanboys complained about Batman Begins or Dark Knight, in fact they LOVED it. Why Matt? Why would the fanboys love it if it deviated so much from comic book continuity?

Because it stayed grounded in the gritty dirty believeable atmosphere that fanboys wanted. As long as they did that the rest were details.

And might I add Michael Bay deviated from Transformers as much as he could. Do you think either of those movies any good? And before anyone goes running for the old standby talking point “It’s a movie based on a toy/cartoon” Batman is a movie based on a comic book about a guy in a costume chasing some dude who is literally a clown.
So you can get off that horse.

Fanboys are not the problem, never have been –and I say that as somebody who hates Stephen King and his “books.” You can use that as a shield for incompetent filmmaking if you want, but it don’t fly out in the world.
If you were right then Sin City should have bombed. Or at least should have been a crappy movie. It wasn’t. It stuck to cannon and audiences in general loved it.
Shouldn’t Lord of the Rings have been the most hated movie ever? It wasn’t. It deviated wildly from the books and fanboys loved it.
So what does that tell you? The “Watchman” effect is all in your mind. Either the material is screen-worthy as-is or it needs to be altered. That has nothing to do with “fanboys.”

If the studio isn’t sure how closely they should/can stick to the material, fine. But don’t give them license to blame their own hesitance –based on their own incompetnece,– on those who are the least responsible for it.
These studio hacks drag their asses just as a matter of course. Doubt me? Then tell me where that Wonder Woman movie is hiding at? Maybe the fanboys have blocked that one too?

BTW, isn’t it interesting how nobody ever says a word about Harry Potter, even though that franchise sticks to book cannon almost word for word. And when they deviated a scintilla with Voldemort the fangirls went nuts?
Still waiting for somebody to eviscerate the fans of Potter for their rabid obsession with the film directly mirroring the books, and why they’re so successful.

Whilst I do tend to be among the baying masses when something I love is adapted I have to confess that the attention the original material gets after a movie comes out almost makes butchering it on the big screen worthwhile! Did you read the graphic novel after? That rules…