Wildlife fences are constructed for lots of reasons, including having them killed by cars (and people along with them) to prevent the spread of disease and to protect small small populations of threatened species.
Near more populated areas, the concern is different; predatory animals will wantonly kill livestock and ruin crops, a few threaten human lives.
Separating people and wildlife by fencing is a mutually beneficial way to avoid detrimental effects but a paper in Science, clearly written by people who clearly do not live near bears, wolves or mountain lions, argues it is a last resort.