DH and I were on a cruise last week that had many, many blue cards. Anytime we asked any of them if they were having a good time, without exception we got an enthusiastic "Yes!"
So as a business, who would you rather cater to: A) New customers who think your product is great (and also spend more money that the average repeat customer) or B) Long time customers who continually complain about your product in public foruma and who aren't as profitable as new customers?
Perhaps the strategy is indeed to get rid of the griping, unprofitable plats and diamonds and replace them with people who actually like cruising with Carnival.