Training is what matters, an untrained dog will kill. If you train your dog it will not, just because you have seen dogs kill birds does not mean the whole breed kills chickens. If someone has a dog and does not train it to be nice around chickens or any other livestock then it will not be nice around them, simple as that. I have seen plenty of dogs kill chickens and every time it was a dog that belonged to someone who did not have chickens and had no need to train their dog to be nice around them. I have a neighbor down the street who has a boxer and a chocolate lab, they also have chickens, both dogs are excellent little girls and are very well trained, they rarely leave the property but when they do nothing happens, they never mess with my chickens or my dogs or even my rabbits, they know there name's very well and are very easy to return to the owner if they come wondering by. Further down the street I have another neighbor who has two labs, they have no chickens but the dogs are still very friendly and well trained but not with chickens and unfortunately they have killed several of my neighbor's birds and a few of mine. Further down the street in the opposite direction I had a neighbor who had 5 large livestock guardian dogs for their alpacas and another neighbor who had a few mixed breeds as pets. The mixed breed owner had goats, guinea hens, and chickens, his dogs were always very nice to my birds if they escaped, the alpaca dogs were not so nice, they killed the mix breed owner's chickens a few times, luckily they were far enough down the street to not venture onto my land and kill my birds. There is another dog breeder on my street to, he breeds Huskies and they are not trained to be nice with chickens but I have only had to worry about that once, he keeps is dogs very secure and they rarely get out.
Another thing that you should watch out for with dogs being around chickens is having untrained dogs with trained dogs, if you have a dog that is nice around chickens then don't let him hang out with dogs that attack them. If your dog sees another one of his buddies mauling a chicken then he might get hyped up and join in to.