In practice, in the US, the categories you listed have all been used as proxies for race and/or ethnicity. Making a claim of discrimination based on proxy chara

In practice, in the US, the categories you listed have all been used as proxies for race and/or ethnicity. Making a claim of discrimination based on proxy characteristics isn't always clear cut, but it sticks often enough to make companies cautious of it. But yeah, fundamentally, in the American system, something needs to either explicitly or implicitly be a protected class. Otherwise it's legal to discriminate based on that characteristic. Plus the list of protected classes varies by jurisdiction.