While I can undersand modern readers seeing Emma as a "snob", It simply does not accord with the realities of the time. Yes she was being a bit haughty in "not speaking to RObert Martin", but if she wished not to speak to him that was her privilege just as it was rude of Mr Collins to try and force himself on Mr Darcy without an introduction. It's true that she does not admit teh worth of the Martins but that is mostly becuase she is trying to detach Harreit from them.
What Mr K objects to is not that Emma is snobbish as such (though he himsef is willing to acknowledge teh worthiness and goodness of the Martin family and to be firendly with Robert) but the fact that she is in some ways "not enough of a snob". She wants to interfere in the class system, to take Harriet out of the class she has been left in, Mrs Goddard's set, and try and bring her up and make her eligible ot marry a fully fledged gentlman...