I think it is counter-productive to personalise the issue. It is the institution I despise, not the people, though I suspect they feel absolutely comfortable with their privileged lifestyle and so would not be the sort of people with whom I'd have much in common.
However, calling anyone a "waste of air" is, in my opinion, rather chilling and akin to saying they, as people, have no right to exist.
The sort of snobbery and, I believe, racism that has been aimed at this couple should, I think, be challenged, whether you agree with their royal status or not because it reinforces and legitimises the same sort of attitudes that are found in wider society.