I'd distinguish between feeling respect and showing respect. I think that it can be important to maintain civility even when we are dealing with people for whom we can feel no respect. I don't think that we should feel that if we do nit sincerely respect someone we should feel obliged to treat them with contempt, even if we feel it.

Sincerity is not something to which we should always give full rein.

I think there is a sense in which we should always feel respect for someone as a human being, but this need not carry over into how we regard them as individuals.