When you assert that something matters, you are expressing a value. But a value does not exist as an objective truth in a vacuum. Rather, a value is something that is held by a person capable of judging.
You can not talk about what matters without talking about the individuals that it matters to.
When you tell me that black lives matter, then I must ask: To whom?
To be realistic, I would expect this to be followed by the loaded question: So you think black lives do not matter?
And I would say: Not to me, no.
And I would expect to be guilt-tripped and shamed a little, back and forth, blah blah yada.
But seriously, why should I – me as an individual – care about black lives? What does that even mean?