Any training aid can be used or ab-used. I know of two dogs whose lives were saved by the use of electric collars.I fully agree that the best way of training a dog is with kindness and reward, after all how does a dog know what you want of him unless he is told, calmly and gently. But unless you can be absolutely certain that your dog will come to heel or sit on an unexpected flock of sheep or a deer then a collar will teach him that these animals BITE! and hard! Especially useful if you have running dogs.
A greyhound bitch I have when out as a pup saw her first herd of cows, turned to look at them and touched the electric fence with her tail. I've never had to call her to heel when we meet cows,she sticks close by my side.
As for the poor old pigs, hopefully the owner of the G. S. has learned just what the dog is capable of and will keep a stricter eye on it. And I do think they should pay any vet.bills if only to reinforce the lesson. I hope piggies are recovering.