Why is racial grouping of diverse ethnicities with different backgrounds still considered acceptable?

[LSLGuy]

I have no real clue, but a few months ago I asserted that “ethnicity” = genes. And got a lot of pushback from possibly more expert folks who said “No; ethnicity is just culture, not genes”. See here and the few subsequent posts for the back-and-forth.

If parliament effectively runs the UK.....what governing body runs England, Scotland etc

IANA expert, but that is a radically different way of defining that term from what I’ve ever understood, read, or heard anyone else say. IME = “Ethnicity” is genes, “culture” is what you behave or learned or practice. So in the terminology I’ve familiar with, your exemplar kid would be 100% indelibly ethnically Polish, but could possibly be culturally English if he really assimilated far more than most and affirmatively rejected the culture of his parents.

I think the most useful outcome of the dialog was learning that these terms probably mean different things in different countries / cultures. Or at least do in the popular usage; academic usage may be more fully standardized.