Then why the discussion? Because there are questions as to whether exposed feet in tight public quarters is appropriate; In other words, it’s questionable.
When something is questionable, polite individuals will err on the side of restraint and consideration of those around them.
But elevating your feet close to someone’s face in a public setting is never considerate. Putting your feet on the table, where people put their hands, where people eat is not just impolite it’s just plain nasty.