I think the core of this atm is that it sounds like it's going along a similar track to colourbind theory.
http://www.psychologytoday.com/blog/...is-form-racism
Thanks to the obvious implications of the link above it instantly makes a bunch of people immediately suspicious even if they can't explain why but at the same time colourblind theory has it's own form of automatic defense. Anyone who criticizes it or points something out related to the theory is totally racist or trolling.
#AllLivesMatter is technically true but it distracts the focus away from the fact that this currently stems from a disproportionate amount of black deaths. It turns it to a more nebulous and less specified thing almost like the purpose colourblind theory serves. It's difficult to point out that the focus was on disproportionate black deaths without ending up looking like you're against all lives mattering due to how our minds tend to categorize as for/against.
I'm probably thinking way too much into this though.