I tend to think that fictional characters can be subject to any sort of re-imagining a writer or director wants...I mean they are fictional, right? The Marvel universe took several characters who were originally white and/or male and recast them with people of different races/ethnicities/genders. Generally not a big deal.
But some characters honestly hit a little differently, especially if they are as ingrained in popular culture as Bond is. A big part of the James Bond character is his white maleness, and while in the 60s and 70s this was a heroic macho feature, in the last couple of decades, the writers have been able to use 007's white male privilege to portray him as a more complex and flawed character. Bond's interactions with a strong female M would certainly not have worked with a female Bond. And they have added more diversity to the cast in recent films (Felix, Moneypenny, more diverse villains, more diverse and more powerful "Bond girls"). It is possible to use Bond's whiteness and his masculinity to tell an engaging story that can still feature diversity and use those elements to expose his flaws and his privilege.
I am all about championing diversity, and more diversity in Hollywood is certainly a good thing...but turning James Bond into a black character or a female character just because...would be pretty lazy.