The “All Lives Matter” response to “Black Lives Matter” is a disingenuous attempt to downplay the fact that the lives of black (and brown) people are undervalued and often ended by the police in the United States. The point of “Black Lives Matter” is not to say that *only* black lives matter, or that black lives matter more, but rather to bring attention to the fact that many police officers and other people routinely act as though the lives of black people don’t matter.
The following links really help drive this point home:
Why you should stop saying “all lives matter,” explained in 9 different ways: https://www.vox.com/2016/7/11/12136140/black-all-lives-matter
The Real Reason White People Say ‘All Lives Matter’: https://www.huffpost.com/entry/dear-fellow-white-people-_b_11109842
Why You Need to Stop Saying “All Lives Matter”: https://www.harpersbazaar.com/culture/politics/a27075028/black-lives-matter-explained/
Why you shouldn’t respond to ‘Black lives matter’ with ‘All lives matter’: https://www.msn.com/en-us/news/us/why-you-shouldnt-respond-to-black-lives-matter-with-all-lives-matter-my-2-cents/ar-BB14ZRog