Because people know domestic dogs can be a threat, they think wolfs must be the same- or worse, because they are wild. Its flawed logic on their part that is not backed up by statistics. . In North America, people realized that in over one hundred years of documentation, there had been no verified human fatality caused by an attack from a healthy wolf.
As for the cattle industry, the Canadian cattle industry has not exactly been brought to its knees by the large wolf presence there.