Personally I think it depends on the situation. What critter is being hunted, how large is the fenced area, how many animals are in there. I don't see a problem with hunting exotics in a large area with a low pop. Those "garunteed hunts" have really given the whole industry a bad name.
Hunting fenced up natives tho is just plain taking a shortcut and missses the whole point of hunting in the first place.