The thing is, when you're changing characters from 50 or so years ago's gender, you're changing (comic book) "history".
Is there any real reason why Doom couldn't be a woman? Or Torch black? Well, no, not really (though I do agree with Nick's point - Doom's story when made into a woman seems horribly cliché right away). The only reason they're (mostly white) (mostly male) is because of the power structure as it was at the time of conception. The only thing you're "hurting" or "changing" is established lore, people's perception of a character,...
The same can sometimes be seen in historical movies and series. Modern takes on things happening in medieval times, the Far West, Roman times, etc etc, have been shoehorning in female characters left and right - we happen to have a patriarchal history, so most "historically important" stuff happened by men - and since history was recorded by men, too, well, we don't always know much about the women. Still, it's a fairly accepted historical fact that the number of female knights in the Crusades can be counted on one hand. Literally - over all the crusades together. Yet every movie made after, say, 1995, will happen to have at least one warmaiden or amazon-like female fighter to break up the sausage fest. During Roman times, women were the masters of the house...But had no power at all outside or in political affairs. Go watch Rome, or Spartacus, and you'll see plenty fairly strong female characters. Most of them are exaggerated versions of characters who really lived and were female, though.
Is "male" an integral port of the personality/character of, say, Emperor Nero? Or Abraham Lincoln? Strictly historically, yes - neither of them could have held the position they did if they were female, not because they'd be weaker but because of the society they lived in. Is making Batman female any better or worse?
I dunno. Yes, one's "real" history and one is fictional history - but in both cases you're, at most, making an "adaptation of" or "based on" story. How many people would freak out over a movie where General Patton's suddenly a woman? Hitler?
Anyway, my point, because once again I've somehow lost my train of thought: while gender, and skin color, and sexual orientation, and a lot of other such variables, aren't necessarily "core" to a character², changing them in opposition to established lore/knowledge/background without a good reason other than "we want more gender X/race X/orientation X/... in our movie" is an ugly, hacky way of dealing with these issues. More modern IPs and characters tend to be more diverse, and there's no reason why "older" characters couldn't meet/fight/... newly written characters - especially in superhero movies, where the opponents tend to change fairly often anyway.
²For some characters, these
are essential and core to their character. Making a movie about MLK or Shaft or Malcolm X and making them white or hispanic would be quite weird
