I have a really good idea exactly where the Carnival disdain started - I was there. It was on the inaugural cruise for Dream, which sailed from New York in November.
During the cruise there was a CC party, and John Heald was expected to attend. He didn't attend - for reasons I do not know.
I do know that everything was ducky - I mean a large group of CC cruisers had paid to be on that 2-day cruise to nowhere. The weather was rough and it was cold outside.
But from that point on - suddenly CC decided they didn't like Carnival Dream as a ship, they also had a lot of criticism of management for "poor planning" for an inaugural cruise, and then John Heald also got knocked for whatever they could think of...
As far as I know things between CC and Carnival have not been the same since then. A lot of people started criticizing Carnival in the boards there, vociferously, and when a Carnival fan/moderator, Host Mach, stuck up for the line the protagonists got rebellious. Eventually they made life so miserable for him he quit. I guess he also banned a number of them because they left and start the FB "Cruise Critic Sucks"
That entire FB site is populated largely by people who hate Carnival, (former) Host Mach and John Heald, (not necessarily in that order).
I'm sorry, but I think such feuding is ridiculous. I have one fault as a moderator, I am not very good at identifying certain people as "real people" - to me every comment is equal and I rarely take note of who said what...
But the upside to that is that I don't get consumed worrying about online relationships.