You are conflating class, as in a stratified privilege hierarchy within a society, with the more usual use "a group of items with a thing in common." For examp

You are conflating class, as in a stratified privilege hierarchy within a society, with the more usual use "a group of items with a thing in common." For example, in a class-action lawsuit, the "class" means "people who claim to have been wronged in the same way by the defendant." A "protected class" in US Law is a group of people you may not discriminate against based upon the "thing they have in common." For example, you if a job requires lifting a 50lb object, you may not eliminate an prospective employee for simply being female. But you may eliminate a prospective employee for being unable to lift a 50lb object.