Yellowstone used to be a great place to watch elk and moose. Wolves have decimated both populations, and it has bled over well past the borders of the park. If you go to Yellowstone now, be prepared to see very few elk, because they are all wolf crap.
I believe that the reason the tree huggers wanted wolves introduced was that in time, prey populations would shrink to the point that human hunters would be stopped from hunting them, and for sure, elk hunting has suffered greatly where ever wolves have been allowed to run amuck.
Wyoming had a 'trophy' season on wolves in the Yellowstone ecosystem, and considered them predators in the rest of the state, and now the tree huggers have got that stopped, at least for now.
I know personally of wolves taking out 30 plus domestic sheep overnight in the Bighorns a couple of years ago. They don't just take the 'weak and the sick', they kill everything they can.
An argument that I have heard from wolf huggers is that the aspen groves are much healthier since the elk populations are down, and I suppose that is true. Aspen trees or elk? I will take elk every time.