Roosters are certainly edible, in the sense that their meat is a nutritious source of protein and fat, and eating it won't poison you. But they are not popular, because their meat is tougher than that of a hen, and doesn't taste as good.
Sometimes, but rarely. Roosters, like most animals, engage in Alpha Male activities, whereby any male who challenges the dominance of another male in a roost must be dealt with. On the other...
It must declare dominancy in order to be the Rooster of choice when it comes time to breed. The roosters will continue to fight until there is only one left. It'll peck apart another rooster to make...