How can a simple statement like “All Lives Matter” be racist, or be taken to be offensive in any way at all? Almost no one disagrees with what those words say on their face: All lives matter. Everyone is valuable. All men are created equal. Right?
The trouble is that no statement can ever be inherently innocuous. Consider this: “The weather was lovely.” What could be a more harmless thing to say? Now let’s use it in a conversation and change the context:
Person A: “I’m so glad you finally got to meet my fiancee. What did you think? Wasn’t she great?”
Person B: “The weather was lovely.”
What is Person B saying here? Person B is saying, “I hate your fiancee.” And being pretty rude about it.
How about “All babies are cute”? So true, and to the extent that it’s not true, it’s telling a little lie to be nice. Again, let’s put it in a conversation:
Person A: “Look at my grandson. Isn’t he the most adorable?”
Person B: “All babies are cute.”
Again, just like that, the neutral sentiment becomes a rude one. “All babies are cute” means “This baby is not particularly cute, or even cute at all.”
This is a basic principle of language and social interaction, and you know it already. When someone says something, and you respond by changing the subject or saying something vague, you are not neutrally expressing your own idea. You are negating or dismissing the thing they have said.
So when an unarmed black person is shot by the police and someone says “Black lives matter,” if you respond by saying “All lives matter,” what you are saying is, “Black lives don’t matter.”
You may not think you are saying that, but you are. The trolls and racists who invented and promoted #AllLivesMatter had exactly that purpose in mind. If that’s not what you’re trying to say, then don’t say it.