Thats wrong to say. Fancy pigeons are put out in prime condition as can be seen by anyone who has been to a show, especially show racers who are breed for their conditoning and soft feather.In most cases the "fat" you describe is in fact muscle which most fancy pigeons carry naturally because of selective breeding. And who is to say a racing pigeon is healthier? I have always heard that you fly hens light, so which is healthier, a pigeon carrying some extra body weight through protein packed nuts or a hen lacking body weight through lack of food. After all, all animals are supposed to carry 12%-20% body fat.
I think anyone who has called plucking the fairy swallows cruel is a hypocrite for the simple reason flying a young bird on darkness is the same idea and is just as "cruel"