Does that apply to fine dining establishments that hold themselves open to all with the wherewithal to pay the tab? You could care less how others might come dressed to an upscale restaurant so long as they did not "intrude into others (sic) personal space" by listening to loud audio? And no restaurant should impose upon would-be customers with anything like a dress code?

Airlines are common carriers and not in a position to be too demanding as to how their customers dress. Still, some would like to see higher standards, ones beyond such minimums as no barefeet, no obscene t-shirts, etc., even if they cannot be enforced. There is nothing to keep others from judging one by their appearance. And if you are completely unselfconscious about your appearance, why do you react to any of this?