They should only be killed if it puts a family or something important in danger, and even then they could just be captured and moved to a new area.
Actually, the only thing wolves could possibly endanger is livestock, and even then, everybody (exception of Native Americans) came here
long after wolves did, so it's really us doing the crime and intruding on the
wolves' land...
I do a lot of research on wolves in my spare time and watch lots of nature documentaries. Wolves were hunted to extinction in Yellowstone; here's a clip from an article on a brief touch on how it happened:
The original wild wolves in Yellowstone were deliberately killed by the federal government during the period when it was government policy to exterminate the wolf everywhere, even inside national parks. The last wild wolves in the Park were killed in 1924 when two pups were killed near the hot spring cone, Soda Butte, near the mouth of the Soda Butte Creek Valley in the NE corner of the Park. A few wolves persisted in Wyoming until 1943 when the last was shot in the Owl Creek Mountains on the Wind River Indian Reservation. Even after this time, occasionally one or two wild wolves did migrate into NW Wyoming, but there is no evidence that they successfully formed packs. From an ecological standpoint, such lone wolves had no influence on the functioning of the Greater Yellowstone Ecosystem. (Ralph Maughan, "History of the Greater Yellowstone wolf restoration")
Here is an image of the Yellowstone Wolf Hunts:

(PBS)
This is why I don't believe in hunting unless absolutely necessary for food (i.e. grocery stores for basic necessities, home far from civilazation, or stranded somewhere) I simply despise the utterly stupid human race, it can just make me sick sometimes...