Yes, you are therefore a member of a well-defined breeding population (deme) and that membership gives us useful information immediately. Not only do you have a greater chance of getting certain diseases, your group also has higher intelligence, with a mean almost a standard deviation higher than gentiles. If race was arbitrary it would not give us predictive validity of that kind.

Science is a "social construct". As is anything else we talk about. Try telling someone with sickle-cell anemia that race is just a social construct.