A very strange claim there? Look at Tripadvisor's reviews on Volcano Bay first and to keep it fair then look at the same site's reviews on Cowfish and Diagon Alley. Now bear in mind Tripadvisor is used for all reviews we're comparing, that way we know there's no Universal haters there just trolling.
Diagon Alley gets great reviews, I wonder why? Is it because people go there and enjoy it and want to share how great it is, if so that goes against the claim that people complain far more than compliment?
Now I realise some may say that Potter has loads of fans and that's why they get so many compliments, they're more disposed to make the effort to give great reviews as they're biased. To counter that I've included the Cowfish reviews too, that's a restaurant chain and as such doesn't have fans in the same way Potter does. Surprisingly there are great reviews after great reviews, people gushing over how great it is. Strange that this happens on the same site frequented by the same people, with these same people complaining about VB? It really disproves the theory that people only complain.