Knightley was able to rise above this -- in his attitude to Robert Martin and in encouraging Emma to visit with Mrs and Miss Bates. As to Harriet's situation, it has only been very recently in our own society that being illigitimate has ceased to be seen as a social barrier (it may have other consequences due to the age and/or lack of education of the parents, but that is not a discussion for this forum). Mr Knightley does have reservations about Harriet's illigitimacy in terms of marriage to Robert Martin, but recognizes that it matters not to Martin, as he is a man in love and so gives his approval for the match. Robert Martin is the one who seems to have the most modern view of Harriet's situation (it is of no importance), while Emma keeps insisting that Harriet must be a gentleman's daughter, IMO to justify her friendship and a potential match with Mr Elton (ofcourse we know that will never happen).