Not from /pol/, and I see where you're coming from, but "race is a social construct" is itself a construct, and not a helpful one. All words and concepts are social constructs. The question is whether this one refers to something real. Say "race is imaginary" or "race cannot be clearly defined," something testable.
People often talk past each other when discussing race, because the word has different meanings. Older Europeans once spoke of the German Race and the Irish Race as two different things, because it wasn't about differences in appearance but differences in culture or ethnicity.
As most Americans use it these days, "Race" refers to human phenotypes. Obviously there is fluidity at the boundaries and there is plenty of mixing. Nevertheless, there are identifiable human populations with distinct genetic physical traits. Each of these phenotypes evolved over thousands of generations in different geographical regions. All descended from the first homo sapiens, who were very probably dark-skinned, as they had evolved in eastern Africa. DNA evidence confirms that those who migrated into Europe interbred slightly with the Neanderthals, who had already adapted to that environment hundreds of thousands of years earlier. And there was some interbreeding in southeast Asia with Denisovan humans who had been there for probably a million years. This interbreeding may or may not account for some phenotype variations, but all of the differences between the races emerged over the last 70,000 years or so, through simple evolutionary adaptation.
The American conception of race is severely distorted, for cultural reasons, when it comes to "black" people. Their "black" encompasses all the distinct races of Africa, and almost any mixed-phenotype human with African ancestry. It's almost like saying people from Japan and Pakistan are the same race.
Nevertheless, race is not imaginary. It's a real thing. Whether race MATTERS, though, is probably imaginary.