In my experience, this negativity is normal behavior on a fan board. People who love, absolutely love, a brand, are usually also the harshest critics and no, they don't have to experienced the product or service.
Fair? Maybe not, but a brand usually has to mess up their product for a long time before true fans turn against them. They tolerate a lot more than a casual consumer. But when things turn sour, they really turn sour.
Usually negativity on boards like this come from a place of love. They want the company to succeed, cause they love the brand, they hate it when the compay fails (in their opinion). They need a place to vent. And that is best done with people who think similar thoughts.
You see it here, but also on boards about movies, theatre, tv shows, books. It is not my thing, but I assume fashion or electronic brands see the same thing on their fan boards.