Really interesting question....
I love nature programs, it is impossible to not appreciate the life of most animals without watching and being fascinated by their predatory strategy and fight for survival. We are animals, we are programed for survival. We certainly hold on to some evolutionary traits such as social behaviour arond alpha males etc. Some also appreciate and respect the physical prowess and physical bility (including fighting) of others.
Evolution alters to fit envroment. We are in interesting times, our enviroment is changing so much faster than our evolution. Although by enlarge humans don't need to be so violent in 2012. We are still interested and intregued by it because of our nature. It isn't a coincidense that its men attending MMA, Boxing, Wrestling, Sumo etc events.
For those believing in God. Violence is built in to every animal. A lion tearing a zebra to shreds on the discovery channel is far worse than two consenting adults fighting for money (food on the table and a house) or prowess (alpha male).
I actually don't enjoy to watch any of this stuff, I may watch a paticularly big fight but even then my interest levels are low. But I get why people do like it. As a trainee medic, I don't think it is a very smart way to go through life but then I love riding motorbikes so who am I to talk....
Snare x