I would say that any voluntarily acquired and freely renounceable attribute is a valid and ethical attribute by which to judge the character of, or discriminate

I would say that any voluntarily acquired and freely renounceable attribute is a valid and ethical attribute by which to judge the character of, or discriminate against, another person. It may or may not be a good idea to do so, but the organizers of a private gathering may exclude whom they wish; the nature of ones employer is not an unethical standard for exclusion.