Mixed race is a term used because people who self identify as mixed race often prefer it to the terms suggested to replace it
Or maybe they like the term mixed race and feel that it describes what they feel they are? you sound as though you are saying they use the term in the absence of something better?
You know what will make the term mixed race meaningless and possibly make some people look for another term?...
White [or any other mono racial] people claiming it as theirs when they are white but just with a white British parent and a white German parent for example. That would mean that person had a mixed ethnicity not race.
I disagree there is no such thing as race.
Ive heard the 'race is a social construct' argument. if anything ethnicity is more of a social construct, if you were the last italian on earth, you would no longer have anyone to share your culture with, but you would still be a white european.
Culture, beliefs, language etc can all be 'removed' for want of a better term, but a persons race doesn't change.
'Race is a social construct' seems to be an idea that is studied by academics with good intentions, but little real life experience of the issues of race and particularly racial identity.
Dreams of a perfect world, where no one is discriminated against is an ideal. But you won't banish racism by denying the existence of race and stating 'we are all the same', it is not our differences that cause racism, so there is no point denying them.