“All Lives Matter” is like a Narcissist trying to bring the spotlight back to them. They can’t stand not having the attention, and will do anything to get it.
We have a movement in Canada called "Every Child Matters" due to indigenous history. The most annoying thing to experience is the same idiots who complain about BLM commenting on this one. "Black Lives Matter? What the hell dude, ALL lives matter!" then 5 minutes later saying "Every Child Matters? No shit, what a stupid movement name!" Can't win with these folks.
I like to think of it like a broken bone. Yes, your overall health is important; no one is questioning that. But if you go into the ER with a broken bone and the doctor tells you that they're going to ignore your injury in favor of telling you to take your vitamins, they're an asshole who doesn't care about your pain or healing your injury.
Systemic racism is the broken bone. No one (except, perhaps, assholes and billionaires) disagrees that all lives have value. Saying "all lives matter" in response to "black lives matter," though, is saying "let's wilfully ignore the problem because I am clearly okay with the status quo."
My favorite analogy for this, and the one that really made me 'get it', was posted on Reddit a number of years ago, and was something to the effect of:
Imagine you're sitting around the dinner table with your family, and your dad is passing around a bowl of mashed potatoes. However, instead of handing it to you, it gets passed right by you to your sister. And you speak up and say, "I should get some, too!" Your dad looks at you and says, "Everyone should get some," and the family continues passing the bowl around as before. And you're thinking, yes, that's true - everyone should get some, but only one of us is not getting any right now and pointing out that everyone should get some doesn't make me any less hungry.
Those people will tell you they’re not racist, that’s why there is no systemic racism. They think you are being racist for singling that out when there was none. Could it be a large part denial, lack of awareness? Or is that just a claim to explain their outrage?
To be fair casting for both Tilda Swinton as The Ancient One and Johnny Depps as Tonto were both criticized when the movies were released. Probably not to the level Halle Baileys casting was, or by the same people, but both were definitely seen as whitewashing.
Its also likely The Ancient Ones casting got as much attention as it did due to the political nature of the change (seen as to appease China over its history regarding Tibet).