I think what they're getting at more than anything is examining and judging the weight of those traditions, and whether or not those traditions are even altogether valid, or worth continuing beyond the sake of simply continuing them as a mindless practice.
Some characters obviously maintain their traditional skin color because that aspect of their character is a fairly key one. Some maintain that tradition for no other reason than it's tradition, and there's no examination of that tradition or where it fits in the larger storytelling possibilities.
As you brought up earlier in the thread: Bond is pretty far removed from Fleming's vision of him, even after the mostly-accurate adaptation of Casino Royale (comparatively speaking, of course), and the name James Bond doesn't really stand for anything beyond "Guy in cool suit with awesome car shoots bad guys and has sex with hot women," and hasn't stood for much more than that for decades now.
So the question is, does Bond's skin color really have anything to do with that conception of the character?
IMO the source material should only be changed if there's a reason for it to be changed - and sometimes, as mentioned, a different ethnic background can evoke different things for a character. Fans are perfectly entitled to demand (within reason - I sympathise with those who didn't want Craig, but the campaign went way over the top) that tradition be respected, because it's that tradition they have emotionally invested in and the creator envisaged for their character. If anyone can tell me a reason why such a conspicuous change as altering James Bond's race NEEDS to happen, why there's anything internally wrong (aka regardless of politics existing outside the fictional world) with keeping him white as he is now, I'd be happy to hear it. As I've said all along, were Idris Elba five years younger, he's got the right gruff charisma, manly looks and acting ability to be great in the role. However, so do Fassbender, Hardy, Stevens, Madden, maybe Sturgess, etc. In the situation where there's no creative need to change the source material, I don't believe in doing so. If people have engaged with a character, keeping that character consistent is not mindless at all. The question is not 'why should we not change this character?', or else you might as well abandon any idea of creative continuity altogether. The question is 'is there any need to change this character?' If the answer is 'yes', do so. If 'no', then don't.
You are right that the modern Bond bares little in common with either the early films or the character Fleming laid out - making him significantly less interesting IMO, but that's totally subjective - but while that means bringing in a black actor certainly wouldn't be as impactful, for lack of a better term, on the role as it would've been back in 't day, it's still a needless change that I think undermines the character as a credible fictional entity. It's as much about the fact Bond has been portrayed as white on-screen already. I have less of a problem if a character's race is changed from the very start, as that's the beginning of a character's screen continuity. It can work with reboots too, though as mentioned before, I generally find rebooting to be an awful practice (again, subjective) and will never advocate for it.
Re: colour-blind casting, the obvious difficulty is that the bulk of popular Western entertainment is based around white straight male characters, meaning that by keeping a lock on those physical attributes, there is a very real and valid concern that, since Hollywood is producing next to no original movies these days, minority actors will have no way of being fairly represented on-screen, a self-perpetuating cycle. I think there are solutions to this, first among them being to give more minority actors the lead roles in blockbuster parts where the protagonists do not have a clearly defined identity, e.g. your Transformers movies, Pirates Of The Caribbean, Fast & Furious (Paul Walker replacement?) Star Wars (fantastic they're doing exactly this), Star Trek (if they ever do a movie/series with a new crew), as well as the few original movies like Interstellar, and indies, which are no less overwhelmingly white. That's not to mention the importance of getting more non-white directors, writers, etc.
Just as whitewashing is rightly loathed and criticised, changing any character's race creates needless antagonism with fans (well, certain fans - there are plenty who don't particularly care or share my views, which is of course perfectly fair) and consequently makes race a conspicuous part of the casting, intentionally or not forcing external politics onto the creative work. There will always be racists out there who just don't want to see minority faces in anything, but casting consistently gives easy arguments to expose those people's prejudices, whereas advocating blind casting for white roles allows them to cloak their hatred in a semi-legitimate point. For me, progress will be being made when minority actors are being fairly represented by enough original lead roles, even (or especially) in existing properties, to be cast 'invisibly'. Colourblind casting does make race an issue and I for one don't see that as being particularly helpful in the bigger picture. (Rant over)
