I think the thing that really exposes the whole constructed nature of race is asking this question; "Is Obama white?"

Barack Obama's mother is white. His father is black. If I were to ask you "Is Obama black?" most people would say yes, of course. He's the first black president after all.. But the moment we flip the question, it suddenly becomes much harder to answer in the affirmative. If someone tried to claim that America has never had a black president, most people would think they were ignorant, an idiot, or insane. Whiteness has always been constructed in a way that relies on purity. Obama is not white, because he's partly black. But being partly white does not prevent him from being black. There's no rational explanation for that. It doesn't conform to any biological notion of taxonomy. It's not about genetics, it's about vibes. We assign whiteness and blackness based on wholly different, wholly arbitrary criteria.

Credit for this example goes to Innuendo Studios who I believe is also where I encountered the proposition that race is a fiction in the same way that money is; it's something we invented, but because we believe it's real, it has real power.

Race matters because it matters. It shouldn't, but it does. Understanding that race is a fiction is a really important step in deconstructing the harms that racism has done, but it doesn't allow us to dismiss the concerns of racialized people, nor should it ever be reason to prevent people from using race as a way to identify themselves. Black people are black because they live the experience of being in a society that treats them as "black" and not simply as "people." That experience is unique to their blackness, even though that blackness is merely a fiction.