Good manners debase you? No, your good manners enhance you, regardless of the response you get from the other person. They can only debase themselves.
Good manners never debase the giver.
However just as manners are a statement, a statement of NOT REWARDING uneducated and purposfully cluless louts is a valid statement.
When was the last time you saw a crew of paris hiltonites give up their seats for an elderly couple? rare if ever.
How about in a quick stop restaurant where the uncouth man continues to wear his hat when his age says he should know better.
Good manners should never be allowed to be used as a leverage against the practitioner.