The point is that we as humans exploit whatever is in our environment to satisfy our own selfish needs or desires. We will do this until we become gluttons of fulfilling our whimsical hungers. Of course, we usually take the least amount of risk in accomplishing our selfish objectives, regardless as to the magnitude of reward.
Fighting one another requires skill, a certain degree of athleticism, and a higher threshold for pain. Paying someone else to fight is another alternative to quench our thirst for aggression, violence, and bloodshed. Capturing other animals and making them fight is just another ploy that we use to entertain ourselves by satisfying our thirst for aggression and violence.
As children, we used to capture butterflies, preying mantis, bumble bees, and wasps. We'd place any combination into a large just to make them fight or eat one another. To us as children, that was fun. If the insects appeared not to be interested in engagement we'd just shake the jar in order to agitate them into an aggressive state. It almost always worked. We'd talk about the fight between various insects for weeks.
It's in our nature to control the variables within our environment to the point that we satisfy all of our senses. Humans have a sense or natural proclivity for both violence and competition. We manifest this desire through wars, hunting, sports, and games.
When we hunt, we satisfy our need for food. We've also out-smarted the prey. When we war, we satisfy our egos and our need to dominate through violence. When we employ the shooting sports, we exhibit our exact capacity or potential for violence using a specific weapon type. When playing games or certain sports, we demonstrate our capacity to use strategies while employing violence and aggression in a more methodical manner.
Fighting cocks and dogs are very low-risk forms of entertainment that satisfies certain humans' thirst or quest for violence. While I don't personally endorse or ascribe to any form of this type of behavior, I do understand its roots.
Vick should be allowd to have a dog! Why not?