Just read an interesting article tackling this very question. I know, for me, the calls for ironclad purity and ire from fans that he mentions seems very, very familiar.

The problem lies in the basic critical conceit that if we go about judging movies based on what we believe is the ‘right’ version of the character, we have doomed anyone from ever trying anything new. You end up with Superman Returns where you get a director who obsessively sticks to the predetermined path another creator has forged. While that might service the fans, it inhibits the idea that someone would create an original take on the character. I don’t know if J.J. Abrams' Superman would have been any good with a Kryptonian Lex Luthor and other assorted deviations. But I think having those things exist is more interesting than watching fans clutch their beloved heroes so tightly that they strangle the potential for something new and different.

Given that reboots and retcons are a constant source of near erosion to the comic book superhero one-act play... does it strike anyone else as strange that, in a fandom where What If?, Elseworlds and new artists and writers are accepted without concern, film interpretations of superheroes are required by fans to adhere so strictly to The Proper Source Material?