You're missing the nuance that while they are invented they are used in real ways and cause real effects. That's what I tried to point out to you in my original response. So your assertion that it's either they are based on nothing or people can say it matters is a false dichotomy. They are invented but also the have been used throughout history to segregate people and cause peope to have differing life experiences. So it's not unjustified for someone to say their race has a lot of impact on their personal life experience and thus identity.