There is a saying, attributed to Oscar Wilde, which goes something like this -
I think, in the general sense, it is accurate. Children start off by loving their parents unconditionally - respect does not come into it. They are weak and vulnerable creatures who depend upon mummy and daddy for their every need - as much psychologically as physically. They will give this unconditional love even in the face of mistreatment - sometimes for the length of their childhood and adolescence. Again - respect as we understand the term, does not feature in this emotional attachment. I loved my mother long before I respected her, and when that respect developed, it was because I understood the things she had done for me, and the sacrifices she had made on my behalf - not simply because she was my biological parent. And even now, I would not show her disrespect, but I do not agree with all her views. So I would disagree with your premise that respect is a due, and does not need to be earned, but I agree that there are sometimes boorish people who justify their behaviour with the 'respect must be earned' excuse.
My own approach being that everyone should be treated with a modicum of respect, until I know them sufficiently to either increase that to complete respect, or to withdraw that respect. Added to which are the layers of societal convention, common courtesy, and consideration for a fellow being - especially if they are elderly, or infirm.