More words = more unwieldy = worse slogan. Besides, nothing in the statement of "Black Lives Matter" implies that other lives don't or that some how black lives matter more. If someone assumes that implication is there, it's because they're projecting their own insecurities onto it.From a pure branding standpoint, the movement may have been better served having been called "Black Lives Matter Too" because "All Lives Matter" was always the logical response. I get that ALM is used by racists to counter BLM but all lives do matter and having to always explain "yes, but" isn't helping (if you're explaining you're losing etc).
Also, I understand what you're trying to say, and not accusing of you of being opposed to BLM (want to make that clear), but to change or weaken a slogan filled with meaning would simply be to capitulate to bad actors who were always going to have a problem with the movement regardless of how it presented itself.