I don't really know what the "Black Lives Matter" movement stands for -- whether it's mostly reasonable, mostly stupid, or whatever. I'd have to Google it to figure that out, which I don't feel like doing.
But I don't have to Google anything to realize how stupid the "All Lives Matter" response is. It's just pedantic trivia.
"Black lives matter."
"ALL lives matter!"
"Squirrels are mammals."
"ALL rodents are mammals!"
"Kristin Cavallari lives in Illinois."
"ALL Chicago residents live in Illinois!"
"My neighbor wrote a book."
"ALL authors write books!"
Actually, this could be decent shtick...